Jacob received his calling while quite young. Like Nephi, Enoch, Joseph Smith, and others, the Lord called him to the work from his youth. Jacob’s righteousness was such that he was privileged to see the Lord and His pre-mortal glory as did Nephi and many other prophets. Peter tried to teach the saints how to reach this degree of spiritual maturity, faith, and purity:
Whereby are given unto us exceeding great and precious promises: that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust.
¶ And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge;
And to knowledge temperance; and to temperance patience; and to patience godliness;
And to godliness brotherly kindness; and to brotherly kindness charity.
For if these things be in you, and abound, they make you that ye shall neither be barren nor unfruitful in the knowledge of our Lord Jesus Christ. (2 Pet 1:4-7)
Joseph Smith taught that the “knowledge” that Peter was talking about was a personal knowledge (Teachings of the Prophet Joseph Smith, p.305). This is what Jacob had received. He had partaken of the divine nature and his knowledge of the Lord Jesus Christ was not unfruitful. DC 93:1 states, Verily, thus saith the Lord: It shall come to pass that every soul who forsaketh his sins and cometh unto me, and calleth on my name, and obeyeth my voice, and keepeth my commandments, shall see my face and know that I am.