"Nor because they are his descendants are they all Abraham's children. On the contrary, "It is through Isaac that your offspring will be reckoned" (Romans 9:7)
Many times we look to the physical world around us to interrupt it. Being human we based everything on our five senses. However as Christians we also have a sixth sense, which is most important for us in the truths of God. We need to use it to filter the world around us and understand what the Bible is speaking to us. This sense is faith. The Israelites were a natural people and they were familiar with God, His principals and His promises to them. However God's promises are spiritual so without faith it is easy to misinterpret them and miss them completely.
God's promise to Abraham's was having a son through Sarah. He rushed fulfillment of this by having a son with Sarah's maidservant Hagar. However, the promise spoken to Abraham was much more than a physical descent, the promise is that Abraham would be the father of many nations and the he would bless the entire world ( Genesis 12:2-3 ). The promise referred to the coming Messiah. It would be through his seed that the Christ came. Paul said in Galatians, "The promises were spoken to Abraham and to his seed. The Scripture does not say "and to seeds," meaning many people, but "and to your seed," meaning one person, who is Christ" ( Galatians 3:16 ). Fulfillment of this promise could only come through his wife Sarah. Abraham had to believe God for this to happen because they were well along in years and Sarah was barren. This took faith and the Bible says that because of it, Abrahams faith was credited to him as righteousness ( Genesis 15:6, Romans 4:3 ).
In today's passage Paul tells us that it is not the natural children that are Abrahams children, but it is children of the promise which came through Isaac. Paul adds clarity to this in Galatians 4, "For it is written that Abraham had two sons, one by the slave woman and the other by the free woman. His son by the slave woman was born in the ordinary way; but his son by the free woman was born as the result of a promise" ( Galatians 4:22-23 ). Remember the promise was that the Messiah would come through his line and bless the world. This blessing came through the birth of Isaac and this came about by faith in what God said. Abraham was justified and made righteous before God on the account of this faith.
The same is true for us who believe in that promise originating with Abraham. If we have faith in Christ as our savior and do not rely on our works to make us right with God, then we are part of Abrahams family and part of this promise. "If you belong to Christ, then you are Abraham's seed, and heirs according to the promise" ( Galatians 3:29 ). What an amazing thing to understand. Through faith in Jesus we do not have to rely on the physical interpretation of God's family, we can rely on his supernatural definition of who his children are. "Therefore, the promise comes by faith, so that it may be by grace and may be guaranteed to all Abraham's offspring-not only to those who are of the law but also to those who are of the faith of Abraham. He is the father of us all" ( Romans 4:16 ).
Faith is the beginning of the adventure. Today I am blessed to be counted among this wonderful promise that Abraham receive of the Lord. Today, I am join with the millions of people who have partaken in the blessedness of his seed, the Messiah. This journey starts with faith by believing in what God has promised us, and it ends with being made righteous and holy before him. Today, I pray that you take the first steps in being reconciled with God through faith in his son Jesus, amen!