It has been narrated from b. 'Abbas that the Messenger of Allah (S) said, “That which is sent forth will be seen and that which is left behind will have the least benefit, and woe upon those people who have left things behind (which will be of no use to them in the next life) - that which they left behind was either an entitlement which they prevented others (from using) or was something worthless which they had collected (to make use of) but it had no benefit.”[1]
If we read this tradition with the verbs as being in the passive form, then its meaning would be, “That which will be sent forth will be seen and that which will be left behind will have the least benefit and woe upon those people who leave things behind (which will be of no use to them in the next life) - that which they leave behind was either an entitlement which they prevented others (from using) or was something worthless which they had collected (to make use of) but had no benefit.”
This tradition points to the material possessions which a person has at his disposal while living in the world. If these possessions are sent forth before hand in preparation for the other life, then according to this tradition, the person will see all of these things there. This same issue can also be seen in various verses of the Qur`an and in one particular verse of the Qur`an in which we read:

إِنَّا أَنْذَرْنَاكُمْ عَذَاباً قَرِيـباً يَوْمَ يَنْظُرُ الْمَرْءُ مَا قَدَّمَتْ يَدَاهُ وَ يَقُولُ الْكَافِرُ يَا لَيْتَنِـي كُنْتُ تُرَاباً

“Verily, We have warned you of a penalty near - the Day when man will see (the deeds) which his hands have sent forth, and the Unbeliever will say, 'Woe unto me! would that I were (mere) dust!'”[2]
A person will definitely see everything that he sent forth for himself - and in other words, this verse clearly alludes to the issue of Tajassumul A'mal or the Physical Manifestation of our Actions - not that the reward or the effects of the act which were done will be seen. Thus, the material benefits which a person delayed in sending forth will have the least amount of benefit for him - especially if he had attained these things through illegitimate means. Thus, the important issues concerning the actions of a person revolve around the training of the soul (just as the topic of this discussion mentions).
Question: What consequence do the actions of a person have (upon him and others)?
Answer: A person's actions have two effects: (1) The external outcome or the societal effects; and (2) the guiding effect on the soul and it is this aspect - the training of the soul - which is the important issue.
Let us suppose that a person gives away something in the way of Allah (SwT) by offering something in charity - we see that this charity has two products or outcomes: The first outcome is that the society is saved from uneasiness and discomfort when the needy person is given a portion of this gift. The other aspect is the training of the souls (through this act of charity). Simply having a person who is willing to give up one's wealth of this world and who is seeking to strengthen the soul by means of sacrifice and piety in the way of Allah (SwT) - this act of his will slowly be transformed from a mere (physical) act into an usual and common action (that one will constantly perform) and in the end, this act of his will become a regular habit and second nature for him.
A great number of actions only see the first aspect (as has been mentioned above). For example, a person may give something in charity, however his intention or purpose is not Allah (SwT) - rather, he performs this act to show off to others. Sometimes it is possible that a person - in order to attract the love of his close friends - and not for Allah (SwT) or for showing off - will perform an act of goodness - thus, this act is done for a reason or goal which does not belong to anyone (neither Allah, nor himself). The effect of this type of charity remains only within the society and it does not have any effect on the soul of a person because it was not done sincerely for Allah (SwT).
It has been seen that there are some people who state the following in relation to their will or bequest, “Even though I myself did not make use of my wealth, however I shall bequest that after my death, my money should be spent for righteous acts.” This person is definitely negligent of the fact that the bequest he made has a weak effect on the training of one's soul even though through this will, he may end up making a group of people rich!
Thus, any good that is done for a person after his death does not result in an honour for him because he gave his wealth to somebody else to do good in his name.
If a person was to bequeath all of his wealth - and even though such a will is not correct (from the Islamic point of view) - however this act still does not have any affect on the training of one's soul.
Thus, after death, what kind of an effect can these acts have on a person?
In a well known tradition from the Messenger of Allah (S) it has been mentioned that a person made his will and stated that after his death, the entire supply of dates which were in his storage tower should be distributed amongst the poor people directly by the Messenger of Allah (S). When the person died, the Prophet (S) acted just as the man had written in the will. When the distribution of the dates had finished, it was noticed that in the corner of the date silo, one withered, dried up date remained.
The Prophet (S) picked up this dry date and said, “If the deceased man had given this one dry date in charity with his own hands, it would have been better for him than giving his entire store-house of dates in charity through my hands.” This is the case since the training of the soul was contained within giving that one dry date by his own hands.
As for that which will truly benefit a person on the Day of Resurrection is a pure heart (Qalb-e-Saleem) just as we read in the Noble Qur`an:

إِلاَّ مَنْ اَتَـى اللٌّهَ بِقَلْبٍ سَلِيمٍ

“Except for the one who comes to Allah with a pure heart (Qalb-e-Saleem)”[3]
The response of the healthy heart can be seen in its outward actions which are a direct result of the inner soul, spirit and etiquette of a person and it is for this reason that we are told that we must make our intentions pure and sincere.[4]
Some people question, “Why do you speak so much about the intention of a person?? Such and such a person built a hospital and no matter what his intention was, what difference does this make? In any case and whatever his intention was, there are thousands of unfortunate and downtrodden people who are making use of the hospital!”
However, this sort of thought is rejected in Islam and such words and opinions are a grave error since this is only in relation to the outward and material aspect of a deed done, however that which is important is the internal aspect of an action, which also has an affect on the training of a person.
We are of the firm belief that all of our actions help him us achieve perfection and reach the ultimate aim and purpose of life which is:

إِلاَّ لِيَعْـبُدُونَ

And this purpose is the worship and cognizance of Allah (SwT).
The fruits of the world of creation are none other than the sincere servants - meaning the perfect human being - and this ultimate goal can not be accomplished except with a pure intention and thus, it has been mentioned in Bihar al-Anwar (volume 76, Page 210) that:

إِنَّمَا الأَعْمَالُ بِالنِّيَّاتِ

“Surely all actions are based on the intention.”
The word here "الأعمال” or actions include all deeds and actions - not only those of 'Ibadat or worship. Thus, if a person was to pay attention to the meaning of this tradition, then one will definitely send things forth for oneself and would not wait for others to perform this task for him.[5]
We see that the food which a person eats can be divided into two categories:
(1) Food which enables one to continue living and
(2) Food which only increases the fat content of one's body and adds to the overall body weight.
In the same way, anything which a person acquires while in this temporal world can also be divided into two categories:
(1) Those things which can help and benefit one (in the next life) and
(2) Those things which only add excess weight to one (and do not benefit one in the next world and one will will have to be accountable for them on the Day of Resurrection).
The extra weight and excess body fat can be withstood by the body even though it is of no benefit to the physical self, however on the Day of Resurrection, a person must also give account of this, just like the wealth which put a person through difficulty and did not benefit one in this world. In other words, there is toil but no benefit; there is accountability, but no advantage. Those people who send things ahead for themselves will benefit from those things, and that which remains behind will not necessarily help them.
Therefore in summary, the most important issue in relation to the training of the soul is sincerity. Whenever the sincerity of a person increases, the effects which they have on one's soul in training will also increase and thus, possessing sincerity is the first step on the path towards attaining spiritual closeness (to Allah (SwT)).
There is a very important treatise concerning Sair wa Suluk (attaining spiritual closeness to Allah (SwT)) which has been attributed to the late Bahrul 'Ulum[6]. In the final section of this work, there are things mentioned which make us think that it has not been written by Bahurul 'Ulum, however the first and second section - meaning almost two-thirds of this treatise expound upon important issues which form the basis of the tradition found on page 22, which states:

مَنْ أَخْلَصَ لِلٌّهِ أَرْبَعِينَ صَـبَاحاً، جَرَتْ يَنَابِيعُ الْحِكْمَةِ مِنْ قَلْبِهِ إِلـى لِسَانِهِ

“One who sincerely dedicates himself to Allah for forty mornings will have springs of wisdom (al-Hikmah) flow from his heart to his tongue.”
Thus in summary, if our actions are not performed with sincerity, then they will be like a lamp which others will be able to benefit from (its light) however, this lamp may burn a person himself and one will not benefit from it in the least. However, if our actions are performed with sincerity, then not only will others benefit from them, but in addition, we too will get the most benefit out of them!

Notes:
[1] Ibid., vol. 74, pg. 179
[2] Surat al-Naba (78), Verse 40
[3] Surat al-Shu`ara (26), Verse 89
[4] In verses 88 and 89 of Suratul Shu`ara, in describing the Day of Resurrection we read that on that Day nothing except a Qalb-e-Saleem will be of any benefit.
The word 'Saleem' which is from the word Salamat has a clear explanation and it means a heart which is far removed from any form of spiritual sickness and ethical and theological corruption. In the Noble Qur’an, inrelation to the hypocrites, it is said:

فِي قُلُوبِهِمْ مَرَضٌ فَزَادَهُمُ اللٌّهُ مَرَضاً
 

“In their hearts is a disease and Allah has increased this disease.” (Surat al-Baqarah (2), Verse 10)
In many meaningful traditions, Qalb-e-Saleem has been introduced in the following manner:
1. In a tradition from Imam Ja`far b. Muhammad as-Sadiq (as) he states that Qalb-e-Saleem is:

وَ كُلُّ قَلْبٍ فِيهِ شِرْكٌ أَوْ شَكٌّ فَهُوَ سَاقِطٌ
 

“And any heart in which there is polytheism or doubt, that heart has (spiritually) plummeted and is of no worth.”
This means that a heart which lacks these things is 'Qalb-e-Saleem'.
2. From another point, we know that having a strong affection to the material aspect of this world and the worship it causes a person to deviate and gravitate towards sins as mentioned that:

حُبُّ الدُّنْيَا رَأْسُ كُلَّ خَطِيئَةٍ
 

“Love for this world is the beginning of all sins.”
Therefore, Qalb-e-Saleem is the heart which is devoid of love for this material world, just as Imam Ja`far b. Muhammad as-Sadiq (as) has stated in another tradition under this same verse of the Qur’an, that:

هُوَ قَلْبُ الَّذي سَلِمَ مِنْ حُبِّ الدُّنْيَا
 

“This is a heart which is safe from the love of the material world.”
3. The final word on this discussion is that Qalb-e-Saleem is that heart in which there are none except Allah (SwT) and this can be seen in the words of Imam Ja`far b. Muhammad as-Sadiq (as) in response to a question which was asked from him in regards to the verse of Qalb-e-Saleem to which he replied:

أَلْقَلْبُ السَّليمُ الَّذي يَلْقى رَبَّهُ، وَ لَيْسَ فِيهِ أَحَدٌ سِوَاهُ
 

“The Qalb-e-Saleem is a heart which meets its Lord and there is none other than Him in that heart.”
It goes without saying that the meaning of Heart in these examples is the soul and essence of a person (and not the physical heart) - (Tafsir-e-Namuna, vol. 15, pp. 273 - 274)
[5] In the words of Sa`di:

برگ عيشى به گور خويش فرست كس نيارد زپس، تو پيش فرست

[6] This work can be read at: http://www.al-islam.org/al-tawhid/sayrsuluk/ (Tr.)