He believed Yahweh

This means he accepted and trusted what Yahweh said was true.

he counted it to him as righteousness

"Yahweh counted Abram's belief as righteousness" or "Yahweh considered Abram righteous because Abram believed him"

Yahweh was reminding Abraham of what he had already done so that Abraham would know that Yahweh had the power to give Abram what he promised him.

"to receive it" or "so that you will possess it"

Abram was asking for more proof that Yahweh would give him the land.