Why were the days of the children of men prolonged? It is so "that they might repent while in the flesh; wherefore, their state became a state of probation, and their time was lengthened, according to the commandments which the Lord God gave unto the children of men. For he gave commandment that all men must repent." Repentance is not just an option; it is a requirement. All people must repent, and that’s why the Doctrine and Covenants, repeatedly says, "Say nothing but repentance unto this generation" (see D&C 6:9; 11:9).
Lehi teaches here that we are in a state of probation. The word probe is identical philologically to prove. It’s a time when we can prove ourselves, not only to God but also to ourselves. It’s a time of testing as to whether we will repent or not. We learn by our experiences, and in our probation we learn the difference between good and evil. For Lehi, there really are only two options. It’s either the Savior or the devil. It’s either happiness or wickedness. It’s either joy or misery. It’s corruption or incorruption. Lehi understands too, however, that we aren’t just being thrown out into the wilderness. He has lived through the wilderness where he has been guided by the Liahona, by the revelations that he has received. He knows that the Lord doesn’t just send his children without resources. This idea connects with the concept of mercy, as in Alma 42, where Alma connects mercy explicitly with God withholding the execution of the judgment. You see, if you commit a sin, if you violate his law, he would be perfectly just if he were to lower the boom on you immediately, right? He doesn’t need further evidence. He knows it all. He doesn’t have to call witnesses. There’s no risk that he would judge improperly. His judgment will be righteous, so why doesn’t he just go ahead? Since he is just, God could have created a world in which as soon as we committed any transgression, we would immediately experience a punishment or a consequence. But that is Satan’s plan, or pretty close to it, isn’t it? When you get slapped real hard and too quickly before you have learned for yourself, you’re being coerced or forced into it.
In verse 21 we learn that the "days of the children of men were prolonged … and their time was lengthened." So that means we have a time on earth to prepare to meet God, a probationary time, a time of testing, a time of repentance. Their time was lengthened. In the beginning they were given lots of years to go through this process and to have many, many children. Methuselah lived 969 years; his days were indeed lengthened. Noah lived 950 years, and Adam lived 930 years. No doubt, their days were lengthened!
Now we have fewer years. We may have 80 or 90 or 79 or 91, or however many years we have, but we still have a probation. We still have a time on earth when it is our time to prepare to meet God.