"Abraham had two sons, the one by a bondmaid, the other by a freewoman." Galatians 4:22
Paul is not dealing with sin in this chapter of Galatians, but with the relation of the natural to the spiritual. The natural must be turned into the spiritual by sacrifice, otherwise a tremendous divorce will be produced in the actual life. Why should God ordain the natural to be sacrificed? God did not. It is not God's order, but His permissive will. God's order was that the natural should be transformed into the spiritual by obedience; it is sin that made it necessary for the natural to be sacrificed.
Abraham had to offer up Ishmael before he offered up Isaac. Some of us are trying to offer up spiritual sacrifices to God before we have sacrificed the natural. The only way in which we can offer a spiritual sacrifice to God is by presenting our bodies a living sacrifice. Sanctification means more than deliverance from sin, it means the deliberate commitment of myself whom God has saved to God, and that I do not care what it costs.
If we do not sacrifice the natural to the spiritual, the natural life will mock at the life of the Son of God in us and produce a continual swither. This is always the result of an undisciplined spiritual nature. We go wrong because we stubbornly refuse to discipline ourselves, physically, morally or mentally. "I wasn't disciplined when I was a child." You must discipline yourself now. If you do not, you will ruin the whole of your personal life for God.
God is not with our natural life while we pamper it; but when we put it out in the desert and resolutely keep it under, then God will be with it; and He will open up wells and oases, and fulfill all His promises for the natural.