The power of the Holy Spirit is not optional but necessary. Without it the children of God simply cannot live the life of heaven on earth. The hindrances are too many and too effective. -- A. W. Tozer
Galatians 5:17 (NLT2) The sinful nature wants to do evil, which is just the opposite of what the Spirit wants. And the Spirit gives us desires that are the opposite of what the sinful nature desires. These two forces are constantly fighting each other, so you are not free to carry out your good intentions.
The Tozer Topical Reader – Volume Two, comp. Ron Eggert, (Camp Hill, PA: WingSpread Publishers, 2007), WORDsearch CROSS e-book, Under: "1199. Spiritual warfare; Holy Spirit: need for".