God fulfills to Abraham the key promise, that Abraham and Sarah will have a son, and then tests Abraham’s faith by commanding him to offer that son. Abraham’s faith in the promise is strong, and he does what God commands, believing that God is able to raise Isaac from the dead if that is necessary for the fulfillment of the promise.
All the history of Abraham shows us the interaction of faith with the promises. Faith receives the promises, and the promises maintain and nurture faith in the trials of life. This is the way God works through the promises of the gospel. Our faith feeds on those promises. When we waver, we must return to those promises for restoration and renewal of hope.