en_tn/gen/17/19.md

No, but Sarah your wife will bear

God said this to correct Abraham's belief that Sarah could not have a son.

you must name him

The word "you" refers to Abraham.

As for Ishmael

The words "As for" show that God is switching from talking about the baby that would be born to talking about Ishmael.

leaders of tribes

"chiefs" or "rulers"

Behold

This can be translated as “Look” or “Listen” or “Pay attention to what I am about to tell you."

I will make him fruitful

This is figurative language that means "I will cause him to have many children."

and will multiply him abundantly

"and I will cause him to have many descendants"

But my covenant I will establish with Isaac

God returned to talking about his covenant and emphasized that it would be with Isaac, not with Ishmael.