Read Genesis 15:1-21
In the Covenant of Works, the condition of that Covenant was the perfect obedience of Adam, humanity's representative head before God. In the Covenant of Grace, the condition was the righteousness of God's Son, Jesus Christ, the representative head of all the elect. Abram was wavering and struggling in his faith concerning God's great promises of the Gospel and the "seed." In Genesis 15, we see the gracious condescending love of God meeting Abram to assure him of the immutable sovereign plan of redemption and every promise made unto Abram. And "Abram believed in the LORD, and he accounted it to him for righteousness." This was not Abram's, but Christ's righteousness being imputed to Abram.