It is a genuine possibility for Christians to deceive themselves. There are many ways in which they might do so—for instance, that’s why we are told to make our calling and election sure (to ourselves, of course: God already knows—in fact, He knew it from all eternity past). There are many other ways to deceive ourselves but, today, I want to mention but one. James is the biblical writer who brings up the matter. He says:
But be doers of the word and not hearers only, deceiving yourselves. (James 1: 22).
How timely is this command since there are those who would question the fact that we should obey God by doing something to improve our Christian lifestyles.
For some, any effort on the part of the Christian to do what God commands is wrong. In one way or another—contemplation of the cross is a current one—we are told not to make efforts on our behalf (that’s the arm of the flesh), but wait for the Spirit of God (or Christ within us) to do what needs to be done to conform to the “word” for us instead of us. That is to say, according to them, sanctification is not a joint effort by the believer and the Spirit to obey the truth, but a submission on the latter’s part, while the Spirit of God takes over completely.
Certainly, progress in the Christian’s life isn’t made apart from the Spirit, Who perfects His truth in us, but His fruit comes only to those who “walk by the Spirit” (Galatians 5:16), which he defines as “living by the Spirit” (v.25). To do so, each must “”examine his own work” (6:4), “work for the good of all (6: 10), and be sure he is carrying “his own load” (v.5), since the Spirit won’t do so for him, instead of him.
The self-deceiver is the one who thinks that it is enough to know the truth, and forgets the many biblical exhortations to “do the truth” (cf. John’s writings in particular).