Right at the beginning of the passage God declares to Abraham that he is Almighty. God is Almighty! He can do whatever he wants to do, without any limitations. That's the first thing he says to Abraham because he's ready to fulfill his promise with Abraham and Sarah that they will have a son. The fact that they were so old made this promise seem much more impossible. But with God nothing is impossible. They had to wait till they were very very old but even their age was not strong enough to keep God from doing this Mighty thing. So I have to ask myself, what does God want to do in and through my life? Am I walking Faithfully with God? What do I believe he can do in and through my life?

Having children at an old age appears to be a common thing as we read about this happening repeatedly in the first part of Genesis before the flood, but by the time we reach Genesis 17, this is no longer normal at all. It is now considered something impossible, but as we see over and over again, there are no limits to the incredible things that God can always do!
Here’s Isaac Man.
https://youtu.be/71fOprgmup4
The principle of the Abrahamic covenant is grace. God adds the fifth letter of the Hebrew alphabet to both Abram and Sarai’s names. Five is the number of grace – unmerited, undeserved, unearned favor. As a result, Abraham is “father of many nations” and Sarah goes from “contentious” to “princess”.
That’s our Hebrew lesson but where God really got my attention in today’s passage is v18 where Abraham cries out what about the son I already have and love deeply – can’t he be the one that the covenant and blessings come through? He knows he’s made a mess and is asking God to bless that mess. Whoa! How many times have I done that … not waiting on the Lord but rushing ahead and when it turns out to be a mess, asking God to bless it anyway. God may turn it into something good in His perfect timing but my prayer shouldn’t be “Bless my mess”, it should be “Lord, have Your way.”