The barren woman of Chapter 54 is God’s people.
How can a barren woman have so many children?
The same way Sarah did. The same way Rachel did. It is all by the power of God.
But this explanation is only partially the answer, for the woman who bears children will not be barren any longer. She will go through labor. And yet, the woman of this chapter remains barren and never goes through labor.
How shall we explain this?
We won’t, and that, really, is the point. God’s people will thrive in a way that is inexplicable to logic and our senses, but they will thrive nonetheless by the power of God. It is a miracle of immense proportions. It is very much like the promise of Isaiah 49:19-21 – “Though you were ruined and made desolate and your land laid waste, now you will be too small for your people, and those who devoured you will be far away. The children born during your bereavement will yet say in your hearing, ‘This place is too small for us; give us more space to live in.’ Then you will say in your heart, ‘Who bore me these? I was bereaved and barren; I was exiled and rejected. Who brought these up? I was left all alone, but these—where have they come from?’ ”
This promise is not without condition, and the next chapter names them: His people must draw near to God, listen to him, seek Him, and submit to His direction. But if His people will do these things, he will make them successful beyond anything anyone could imagine, beyond any natural explanation.