Against all hope, Abraham in hope believed and so became the father of many nations, just as it had been said to him, "So shall your offspring be." Without weakening in his faith, he faced the fact that his body was as good as dead-since he was about a hundred years old-and that Sarah's womb was also dead. Yet he did not waver through unbelief regarding the promise of God, but was strengthened in his faith and gave glory to God, being fully persuaded that God had power to do what he had promised.
Romans 4:18-21

This is the time of year when Christians celebrate the birth of the Christ- Child. The New Testament describes the birth of Christ as a miracle, a virgin conceived, that is not the normal way babies are brought into this world. Roughly 2100 hundred years before Christ, there was another “unusual” birth - the birth of Isaac. 

Isaac’s birth was “unusual” but not miraculous or supernatural. In that all the natural elements of conception had to be in play for Isaac to be Abraham’s and Sarah’s son. Jesus’ father was God, not Joseph. The natural process of conception was suspended and a supernatural process replaced it, just this one time.

Now in Romans 4, the apostle Paul, is writing a commentary on Abrahams life to show that justification by faith is not a new doctrine in the New Testament, but in fact it is well established in the Old Testament beginning with Abraham. 

 Paul writes that Abraham “faced the fact that his body was a good as dead”. The facts of life were all lined up against what God was telling Abraham. God said, “you are going to have a son”. The facts of life were that Abraham and Sarah were both too old to become parents. Paul’s writing is so precise, he points out that Abraham faced the facts “without weakening in his faith”. That is where we tend to struggle. We become so full of faith that we are just fools, or we become so mesmerized by the facts that our faith weakens. Balance on this issue is vital.