Because the carnal mind [is] enmity against God: for it is not subject to the law of God, neither indeed can be.
Note 16 at Ro 8:7: This word "carnal" is translated from the same Greek word as "flesh" (see note 13 at Ro 8:6). Just as with the word "flesh" (see note 3 at Ro 7:18), there is more than one way that the word "carnal" is used. All sin is carnal, but not all carnality is sin. The word "carnal" can also refer to human ability or natural things.
Trying to live the Christian life from our own ability is carnal. In context, Paul was contrasting the hopeless struggle of the flesh to live holy, which he described in Ro 7:15-24, with the Spirit-filled life that he presented in Ro 8. Therefore, he was portraying that trying to obtain holiness through the flesh is being carnal. It is inaccurate to think that only sin is carnal. All our self-righteousness is carnal too.
Note 17 at Ro 8:7: The carnal mind is hostile or opposed to God. The carnal mind hates the things of God. Therefore, no one just naturally pleases God. It is impossible for the natural mind to think in the ways of God. As Paul said in 1Co 2:14, "But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned." We have to deny our natural way of thinking and be led by the Spirit of God in order to walk pleasing to God.