This question emanates from incorrect notion about the concept of infallibility that considers it something mandatory and gifted by God without a cause or reason. Obviously, if we are to consider infallibility as something forced, then we would consider the infallibles as people lacking free will and autonomy and that they are like automatic entities that are not worthy of becoming role models for others, nor are they then entitled to any rewards. This is an erroneous perception and understanding of the concept of infallibility since it subscribes to a one-dimensional opinion about infallibility whereas, in fact, infallibility according to Shiite scholars has never been a deterministic issue. They always believe that the infallible imams, abstains from sins of their own free will and choice. For example, Allamah Muzaffar says in his "'Aqaed al-Imamiyah" (Shiite Beliefs):
«ومن الامور التی یجب التنبیه علیها ایضاً هو ان المعصوم (ع) لیس مجبوراً علی فعل الطاعات و ترک المعاصی، و انما فعل و ترک باختیاره؛ لانّ العصمة ملکة و بصیرة فی الامور؛ اذ انه ینفر من المعاصی و یبتعد عنها، و یتشوّق الی الطاعة فیعملها، و کل ذلک بتوفیق من الله عز و جل."[i]
Among the issues necessary to mention is that the Infallible (AS) is not compelled to obey God and avoid sins; they do everything and avoid sins of their free will because infallibility is a second habit or insight about things. The Infallible (AS) hates sins and he avoids them without compulsion; he is desirous of obeying Allah in every matter. In fact, all of this is due to success granted by Allah.[ii]
As well, Allamah Tabatabai has made reference to the same point in Tafsir al-Mizan: "The Infallibles (AS) abstain from sins and obscene things of their own free will and choice. If we are attributing such an abstention to their infallibility, it is like a fallible human being's abstention which is owing to God granting them success."[iii]
Thus, infallibility is a matter of free will and it is for the same reason that it is considered to be perfection. Sinning is not essentially impossible for an infallible but it does not practically happen owing to the power of knowledge and piety.
The fact that infallibility is not essential or forced is not in disharmony with what some scholars have said in theological books about infallibility being a gift of God. That is because although infallibility is a divine gift, but since God knew that they are different from others in terms of the degree of sincerity and devotion, so He bestowed this gift upon them. In other words, the real and lofty value which the Infallibles have is related to things about which the Infallibles are free to act. They include accepting the divine gift and going through difficulties and tribulations which are characteristic of this position. This divine gift (infallibility) is simply a divine confirmation of them. It is not true to say that the Infallibles (AS) were compelled to obey them or to avoid sins which would make them inappropriate as role models. In fact, they were faced with the most difficult divine tribulations and possessed all regular human traits, yet they attained the highest degree of sanctity, purity, piety and perfection.
In other words, what is understood from religious texts is that man's existence and life are not confined to a few years in this material world. In fact, man's soul is created long before the creation of the body.[iv] Hence, the decisions and past reflections as well as God's foreknowledge of the future of men and of who will be in the right or in the wrong path all in all serve as causes helping him get honor, reverence and privileges including infallibility, knowledge, prophethood, imamate, revelation and so forth. Therefore, the belief that the infallibles (AS) have been infallible even in their childhood will not encounter any problems because this endowed trait is based on the knowledge which God, the Exalted, has of the Infallibles that they will not commit any sins in future of their own free will. For further information in this regard, see the following indexes:
Infallibility of ordinary human beings, 104 (site: 861).
Meaning of Infallibility, 1738 (site: 1885).
The Concept of Infallibility and the Possibility of Infallibility of Individuals, 249 (site: 1954).

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