Romans 8:5-6
In fact, those who are according to the flesh think the things of the flesh, but those who are according to the spirit can think the things of the spirit. So the thinking of the flesh is death, but the thinking of the spirit is life and peace.
The flesh is the sin nature inherited from Adam. Thinking the things of the flesh is death. A person who isn’t born again can only think the things of the flesh. Since we have believed on Jesus Christ and received the gift of Holy Spirit from God, we can now think the things of the Spirit. We can meditate on the things that God’s Word tells us we now have and are in Christ. That type of thinking will produce life and peace.
Galatians 5:16
Now I say, walk by means of the spirit, and you will in no way carry out the craving of the flesh.
When we live by the spirit nature we received from God when we got born again, thinking on those things and walking in them, we won’t be thinking about and doing the things of the evil sin nature. That’s very important, because Galatians also tells us of the awful fruit that living according to the flesh produces, and it tells us of the wonderful fruit that living according to the spirit produces:
Galatians 5:19-23
Now the works of the flesh are evident, which are fornication, uncleanness, unbridled lust, idolatry, sorcery, hostilities, strife, jealousy, hot tempers, factious strifes, divisions, sects, envy, drunkenness, carousing, and such things like these. I say to you ahead of time, even as I said previously, that they who practice such things will not inherit the kingdom of God. However, the fruit of the spirit is love, joy, peace, long-suffering, kindness, goodness, believing, meekness, self-control. Against such things there is no law.