What does Genesis 5:16 mean?

Mahalalel had more sons and more daughters and lived another 830 years after fathering Jared. The fact that he is listed as having additional children is important for several reasons. First and foremost, it reminds us that the names listed here are not necessarily the firstborn of any of these men. This passage is meant to trace the lineage of Noah, from Adam. As such, it only lists those names which are in that direct line. Some of these might have been firstborn, while some might have been later.

The idea of these man having other children also supports the idea of a rapid growth in human population. In a modern environment, a population where women average 3 to 4 children each is capable of growing very quickly. In a scenario where people can have children over several centuries, rather than two or three decades, this means an incredibly fast explosion in population.