The Christian walk is a continual process that begins with faith and ends in love (2 Peter 1:5-11). Once a person is “born again,” they receive the Spirit of God. This results in the believer having two natures, the flesh or “the old man,” and the Spirit or “the new man.”
Every time a believer makes a decision, they have to decide whether to make it based on the old flesh nature or the new Spirit nature. “I say then: Walk in the Spirit, and you shall not fulfill the lust of the flesh. For the flesh lusts against the Spirit, and the Spirit against the flesh; and these are contrary to one another, so that you do not do the things that you wish (Galations 5:16-17, see also verses 18-25).”