The Lord revealed three reasons to Mormon explaining why children do not need to be baptized. The first was that little children were not capable of committing sin. The second was that the Atonement of Christ had paid for the transgressions of little children, and the third was that little children could not repent. These three reasons will be considered separately.
Mormon was told that little children are not capable of committing sin (v. 8). After being reminded of Jesus’ teaching that he came into the world not to call the righteous but sinners to repentance (see Mark 2:17), Mormon was told that the curse of Adam (the fall into an environment of sin) was taken from the children, and Satan had no power over them (Moroni 8:8). In the words of modern revelation, “they cannot sin, for power is not given unto Satan to tempt little children, until they begin to become accountable before me” (D&C 29:47). Furthermore, Mormon was informed that the law of circumcision had been done away or fulfilled by Christ (Moroni 8:8). Prior to the Savior’s advent, the law of circumcision was given to teach of his coming to atone for the sins of those who are accountable, and for the transgressions of those who are not accountable. When the Atonement was completed, the law was fulfilled. Thus Mormon concluded that it is solemn mockery to baptize little children when the Atonement of Christ has taken care of whatever transgressions they may have committed (v. 9).
In “A vision [of the celestial kingdom] given to Joseph Smith the prophet, in the temple at Kirtland, Ohio, January 21, 1836,” he saw several people there, some of the past and others who were still alive. “And [he] also beheld that all children who die before they arrive at the years of accountability are saved in the celestial kingdom of heaven” (D&C 137 section heading and v. 10). The age at which accountability begins was revealed to the Prophet over five years earlier, November 1831, when the Lord told him that parents are responsible to teach their children “to understand the doctrine of repentance, faith in Christ the Son of the living God, and of baptism and the gift of the Holy Ghost by the laying on of hands, when eight years old” (D&C 68:25). This revelation confirms the age of accountability revealed to Abraham as quoted above.
Mormon admonished his missionary son to teach “repentance and baptism unto those who are accountable and capable of committing sin; yea teach parents that they must repent and be baptized, and humble themselves as their little children” (Moroni 8:10). Jesus taught similar things during his mortal ministry.
2 And Jesus called a little child unto him, and set him in the midst of them,
3 And said, Verily I say unto you, Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven.
4 Whosoever therefore shall humble himself as this little child, the same is greatest in the kingdom of heaven.
5 And whoso shall receive one such little child in my name receiveth me.
6 But whoso shall offend one of these little ones which believe in me, it were better for him that a millstone were hanged about his neck, and that he were drowned in the depth of the sea. [Matthew 18:2–6]
The Apostle Paul taught the saints: “Be not children in understanding: howbeit in malice be ye children, but in understanding be men” (1 Corinthians 14:20).
Little children are alive in Christ from the foundation of the world (Moroni 8:12). The plan of salvation was based upon the foreknowledge of God. God knowing that many little children would die or be killed due to disease, accidents, and even infanticide because of the agency of man, provided the Atonement for their eternal salvation without the need for baptism (vv. 11–12). If God had not provided for these little children, it would have rendered God “a partial God.” For God to not know which of these little children would die before they were accountable would require him to be changeable and a respecter of persons for “many little children have died without receiving baptism” (v. 12). Wherefore, based on his foreknowledge, God sent those spirits who were of a celestial character to the bodies of those who would die in their infancy. In the words of Joseph Smith:
We have again the warning voice sounded in our midst, which shows the uncertainty of human life; and in my leisure moments I have meditated upon the subject, and asked the question, why it is that infants, innocent children, are taken away from us, especially those that seem to be the most intelligent and interesting. The strongest reasons that present themselves to my mind are these: This world is a very wicked world; and it is a proverb that the “world grows weaker and wiser”; if that is the case, the world grows more wicked and corrupt. In the earlier ages of the world a righteous man, and a man of God and of intelligence, had a better chance to do good, to be believed and received than at the present day; but in these days such a man is much opposed and persecuted by most of the inhabitants of the earth, and he has much sorrow to pass through here. The Lord takes many away even in infancy, that they may escape the envy of man, and the sorrows and evils of this present world; they were too pure, too lovely, to live on earth; therefore, if rightly considered, instead of mourning we have reason to rejoice as they are delivered from evil, and we shall soon have them again. [TPJS, 196–97]
All these children needed was to get a body that they might go on in their eternal progression. Of course other great and noble spirits were needed to administer the plan of salvation upon the earth, and were also chosen in the premortal council to be leaders on the earth at various times in mortality (see Abraham 3:22–23). In the wisdom and foreknowledge of God, the assignments were made based upon the faith and good works of the spirits in the first place or estate, meaning the premortal life (see Alma 13:1–5). Without an acceptance of the omniscience of God, the doctrine of salvation for little children is incompatible with God being unchangeable and no respecter of persons (Moroni 8:18).