Genesis 15:2
And Abram said, Lord GOD, what wilt thou give me, seeing I go childless, and the steward of my house is this Eliezer of Damascus? And Abram said, Lord GOD, what wilt thou give me, seeing I go childless, and the steward of my house is this Eliezer of Damascus?
Abram was distressed and troubled that he remained childless with no child to inherit, and no child to inherit God's promise. He asked God what He would give him while he remained in that childless state. The one standing to inherit his household and possessions was Eliezer of Damascus, the steward and trusted servant of his house.
Abram expected that Eliezer might become his heir. He proposed that Eliezer become his heir by adoption. God answered that Eliezer would not be his heir, because Abram would have a son of his own who would be his heir.
The promise of a son tested whether Abram would trust God's power. Turning to Hagar to bring the promise about, by taking her as a wife, showed that Abraham and Sarah did not fully trust it.