Abraham is a rock (Isaiah 51). What does that mean?

He’s a chip off the Rock of Israel, Yahweh himself.

No matter how much you water them, rocks don’t grow into rock gardens, but Abraham becomes a garden because He is blessed by the Lord.

Abraham the rock grows to become a mountain that fills the earth. Abraham the rock multiplies to become sand on the seashore.

Abraham the rock is the prototype of Petra the rock, on whom Jesus builds His church, the household of Abraham.