Should It Really Surprise Us?

And God said to Abraham, "As for Sarai your wife, you shall not call her name Sarai, but Sarah shall be her name. I will bless her, and moreover, I will give you a son by her. I will bless her, and she shall become nations; kings of people shall come from her." Then Abraham fell on his face and laughed and said to himself, "Shall a child be born to a man who is a hundred years old? Shall Sarah, who is ninety years old, bear a child?"
Genesis 17:15-17

The following is an imaginative reflection of part of what Abraham might have said to Sarah after this encounter with the Lord.

I know, Sarah. We are powerless to have children, now more than ever. But if we've learned anything these twenty-five years, it's that our hope doesn't rest on our power to do anything. Our hope rests on the Lord's power. Our entire lives are built on what he's promised. And the lives of our descendants must be built on his promises for generations before they ever occupy this land. Their survival will depend on them trusting the Lord's promises and not their own power. Should it really surprise us that the first descendant the Lord gives us is a reminder of this?
--Jon Bloom, Things Not Seen: A Fresh Look at Old Stories of Trusting God's Promises

As those living on this side of history, it shouldn't surprise us. Through all their waiting and believing against hope (Romans 4:18), God was forging in Abraham and Sarah the faith that they would bequeath to their descendants ... including us.

When God wants to drill a man,
And thrill a man,
And skill a man
When God wants to mold a man
To play the noblest part;

When He yearns with all His heart
To create so great and bold a man
That all the world shall be amazed,
Watch His methods, watch His ways!

How He ruthlessly perfects
Whom He royally elects!
How He hammers him and hurts him,
And with mighty blows converts him

Into trial shapes of clay which
Only God understands;
While his tortured heart is crying
And he lifts beseeching hands!

How He bends but never breaks
When his good He undertakes;
How He uses whom He chooses,
And which every purpose fuses him;
By every act induces him
To try His splendor out-
God knows what He’s about.

– Anonymous

He knows what He's about.

Know then that it is those of faith who are the sons of Abraham.
Galatians 3:7