Now you, brothers, like Isaac, are children of promise. But just as at that time he who was born according to the flesh persecuted him who was born according to the Spirit, so also it is now. But what does the Scripture say? “Cast out the slave woman and her son, for the son of the slave woman shall not inherit with the son of the free woman.” So, brothers, we are not children of the slave but of the free woman.
We could say that Abraham was a man of practical considerations. We also could say that Abraham was a man of unnecessary worry and presumption. He had received a promise from God, but that promise seemed highly unlikely. There were many physical and factual obstacles to its completion. The natural perspective would bring anyone to a state of doubt. The spiritual perspective, on the other hand, should lead to wonder and anticipation at the seemingly impossible promise being fulfilled. The impossible promise that was Isaac is exactly what we are. Apparently lost and detached from the Lord beyond hope, we have been saved and become children of the most high God.
There are two kinds of birth in this world. Physical birth is what brings us into a state of sin and imperfection. Each of us experiences this birth, and no inheritance comes by virtue of it. If left unchanged, this state leads to spiritual death, damnation and destruction. Spiritual birth is the opposing state. This is a rebirth, which means that it replaces the first. Where we first were born guilty, we are reborn righteous. Where we first were born undeserving, we are reborn worthy. This rebirth sets us free from that once certain terrible end, and that freedom comes with a promise. To be reborn free gives us the right to inherit from the Father through whom we obtain that freedom.
When those we love have left us, we might be left with riches we never thought we would have. Yet, even if someone were to leave us all the riches of the world, that inheritance eventually would be revealed as worthless. It does not extend our days. It does not keep us alive. Its value is temporary. The only inheritance with real value is the one which imparts spiritual riches and takes us from death to life. The inheritance we have through our heavenly Father is an eternal gift. It is only by the Father’s grace that He has freed us from our bondage and made this gift available to us. Father, thank You for the inheritance we gain through our sonship in You.