“The power of the Spirit is strongly manifested in the lives of both Isaac and Christians. Isaac’s miraculous birth took place when Abraham was 100 and Sarah was 90. Paul says in Romans 4:19-20 that Abraham contemplated his own body and Sarah’s womb and realized that they were both basically dead as far as producing children was concerned. It was humanly and physically impossible for them to have children together, yet Abraham did not waiver in unbelief but grew strong in faith and trusted God to give what he promised. Thus, by the supernatural power of the Spirit, Abraham and Sarah were enabled to have a baby boy. His birth was not according to the physical powers of the flesh in that the flesh was unable to produce his conception. It was the power of the Holy Spirit through faith that made Isaac a ‘child of promise.’ It is the same with believers today. Believers, like Isaac, are children of promise, because they too have gone through a supernatural birth. They have been supernaturally born again by the Spirit of God. This is another strong argument that Paul is not thinking in terms of the genealogical principle of natural childbirth when it comes to defining who now are the ‘children of promise.’ In the New Covenant, the children of promise are those born supernaturally according to the Spirit, not according to the flesh (verse 29).”
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