Genesis 17

“And I will establish My covenant between Me and you and your descendants after you in their generations, for an everlasting covenant, to be God to you and your descendants after you. Also I give to you and your descendants after you the land in which you are a stranger, all the land of Canaan, as an everlasting possession; and I will be their God.” And God said to Abraham: “As for you, you shall keep My covenant, you and your descendants after you throughout their generations. This is My covenant which you shall keep, between Me and you and your descendants after you: Every male child among you shall be circumcised; and you shall be circumcised in the flesh of your foreskins, and it shall be a sign of the covenant between Me and you. He who is eight days old among you shall be circumcised, every male child in your generations, he who is born in your house or bought with money from any foreigner who is not your descendant. He who is born in your house and he who is bought with your money must be circumcised, and My covenant shall be in your flesh for an everlasting covenant. And the uncircumcised male child, who is not circumcised in the flesh of his foreskin, that person shall be cut off from his people; he has broken My covenant.” Genesis 17:7-14 NKJV

God established the covenant of circumcision with Abraham and his descendants.  This was an agreement or contract where Abraham gave up some of his flesh through circumcision.  In return, God promised him countless descendants, some of them kings, and promised to be a God to Abraham and all his descendants. Circumcision was an outward act that symbolized an inner transformation.  For Abraham it was a sign of his faith in God.  Circumcision is not a requirement when you become a Christian.  God is much more concerned about our inner lives than He is about an outward sign that may have no real heart behind it.  He desires “truth in our inner being” (Psalms 51:6), and purity of our thoughts, motives and attitudes.

Then Abraham fell on his face and laughed, and said in his heart, “Shall a child be born to a man who is one hundred years old? And shall Sarah, who is ninety years old, bear a child?” Genesis 17:17 NKJV

Even Abraham, who was a man of great faith, had doubts. God was promising him something that seemed ridiculous, even impossible. What has God promised you that seems impossible? There is nothing wrong with doubt.  Everyone has doubts. As long as you have a tiny amount of faith (“a mustard seed of faith” Matthew 17:20), no matter how much doubt you have, God can still show up. For some examples of believers with a mustard seed of faith where God still showed up, look at doubting Thomas (John 20:24-29) or the disciples on the Road to Emmaus (Luke 24:13-35).  Another example is when the disciples were praying for Peter when he was in prison. They did not believe that it was him when he showed up at the door. Deep down they did not think God could save Peter, but they still prayed and had some faith (Acts 12:12-17).