Our life with God is conditional. Because we accept Jesus as Lord and listen to His words the faith of Jesus makes us children of God. God through an angel said to Abraham; “since you have done this thing and have not withheld your son, your only son ” Abraham fulfilled the condition that God had set, that Abraham believed God and did as he was told.
Sand and stars
Abraham didn’t have the Bible, we are lucky; we have all the conditions written down in a book, we can find out what is expected of us by reading, praying and studying. Abraham gave God the best he had and his God, YaHaWaH responded by promising Abraham to greatly bless him and multiply his descendants like the sand of seashores and like the stars on the sky and to defeat their enemies.
And the angel ended his speech by saying; “Through your seed, all the nations of the earth shall be blessed” God said that Jesus Christ would descend from Abraham and through Him God would bless the whole world.