God commands Abram to walk before Him and to be blameless and God made a covenant with Abram. God changed Abram’s name to Abraham, a father of many nations. God promised Abraham yet again that he would be fruitful and have many descendants, and that kings shall come from him. Gods covenant is for Abraham and all of his descendants after him and their generations for an everlasting covenant. To keep this covenant Abraham had to circumcise all of the men in his household, including himself as a sign of the covenant and a symbol to show cutting off the old life of sin to purify ones heart and dedicate themselves to God.
God then told Abraham that Sarai is to be called Sarah now, and she will give birth to a son and shall be a mother of many nations. Abraham laughed at this and doubted God because of their age. It wasn't “normal” for a woman in her nineties to birth a child, but what Abraham was forgetting was that God didn't live by normal circumstances. He is the great I am and can make the impossible possible. God made it clear, that although Ishmael would indeed be blessed, the covenant would be made through Abraham and Sarah’s sons, Isaac. Abraham followed Gods command and circumcised everything in his home that day. Its important to see the way God sees, rather than the way the world does. It is fleshly and worldly to think, “No way will a woman in her nineties have a baby.” But to see things spiritually and to realize God has full control and can make anything happen no matter how crazy it may seem is the kind of thinking and seeing we need to have. Focus on seeing the way God sees with your spiritual eyes and try not to see the way the world does. Seek Gods word and read Gods word to see what the truth is in our lives rather than the facts the world goes by. As a follower of God you have the blessing to live according to His promises, don’t give that up for how the world sees things.