The human mind is more deceitful than anything else. It is incurably bad. Who can understand it? (Jeremiah 17.9 NET)
Finally, brothers and sisters, whatever is true, whatever is worthy of respect, whatever is just, whatever is pure, whatever is lovely, whatever is commendable, if something is excellent or praiseworthy, think about these things. (Philippians 4.8 NET)
No one should believe lies, let alone Christians. Christians are, however, not immune to having evil thoughts. Do I think that evil spirits put thoughts into our hearts? Not necessarily. Christians continue to have a battle with the “fleshly mind” (Rom. 8.6), and are influenced by evil thoughts if they believe the original liar whom humans, in Adam, chose to follow in Eden: But to Adam he said, “Because you obeyed your wife and ate from the tree about which I commanded you, ‘You must not eat from it,’ (Gen. 3.17a NET).
We can lie to ourselves in several ways instead of “thinking about true things” (Phil. 4.8). Don’t listen to your evil heart or other lies from people who are bold enough to spout them. Christians are running in a race against the mind of the flesh (see 1 Cor. 9.24-27). Romans sets out a pattern for us to follow:
For those who live according to the flesh have their outlook shaped by the things of the flesh, but those who live according to the Spirit have their outlook shaped by the things of the Spirit. For the outlook of the flesh is death, but the outlook of the Spirit is life and peace, because the outlook of the flesh is hostile to God, for it does not submit to the law of God, nor is it able to do so. Those who are in the flesh cannot please God. You, however, are not in the flesh but in the Spirit, if indeed the Spirit of God lives in you. Now if anyone does not have the Spirit of Christ, this person does not belong to him. (Rom. 8.5-9 NET)