Again, Noah is blessed by God and given instruction to be fruitful, to multiply, and the fill the earth, in precisely the same terms as at creation (Genesis 1:28). Here is the great command, from the time of the Garden of Eden and the expulsion of the human race, now renewed to Noah.
Some people say that this is a procreation mandate, and all Christians should have families as big as it is possible to have. This and the same command given in Genesis 1, they say, constitute a procreation mandate. We acknowledge that large families are very wonderful, and children are always wonderful, and we would not want to say anything which would cast a shadow over large families, but this is not a procreation mandate. It is not saying that everyone must have very large families. That should be obvious from the context, because, here, Noah has three sons with their wives, and each of them is roughly a hundred years of age, and they have not had a single child between them yet, and did not have huge numbers of children after this. Noah was six hundred, two thirds of the way through his life, and he has only had three sons, and there is no record of him having any more later. So, although there were some very large families in those days, they were not exactly generations of huge families themselves. So it does not make any sense to interpret those words as some people, I think unnecessarily do, as though every one of us must have a dozen children.
Our King James Version says ‘replenish’, and that is a possible translation. But the word translated replenish comes from the verb ‘to fill’. The majority of translations translate it ‘fill the earth’. Our translators have chosen ‘replenish’, which is possible, and legitimate, because they have observed the context – the earth having had its population destroyed with the exception of eight people – and so ‘replenish’, ‘fill the earth once again’, seems to be in mind. But it is very important in these chapters to bear in mind that it also can be translated, and maybe should be, ‘fill the earth’. These words set the scene for what follows in chapter 11 – Babel and the confusion of tongues and the scattering of the people – in which they disobeyed the command of God to fill the earth. The families were intended not only to reproduce, but to spread; not to stay in one place, but to spread through the world and populate it. Because of Babel, that did not happen. ‘Fill the earth’, they were told, and they rebelled against that. At Babel, it is specifically said that they wished under Nimrod to build Babel and the Tower of Babel, lest they should be scattered. So bearing that in mind, the command is made clear, to fill the earth.