For it is written that Abraham had two sons: the one by a bondwoman, the other by a freewoman

Galatians 4:22
For it is written that Abraham had two sons: the one by a bondwoman, the other by a freewoman.

We need to sacrifice the natural to gain spiritual. It is not because God designed it this way so that the natural has to be sacrificed to gain the spiritual. The natural itself is created by God. However, when sin entered the world, it has taken hold of the natural. Without sacrificing the natural sinful nature, we will continue to have a divided life. The natural life will continue to resist the life led by the Holy Spirit. The result of this is internal turmoil. So unless we discipline and sacrifice our life of sin, it will ruin our entire personal life with God.