God is a Spirit: and they that worship him must worship him in spirit and in truth. John 4:24
It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life. John 6:63
But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me: John 15:23
Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, that shall he speak: and he will shew you things to come. John 16:13
Honesty.
Truth.
Deceit.
Lies.
Self.
Deceit.
Alone these words are bad enough, but when these two words are joined together -- Self-deceit/ self-deception -- sin cannot help but be present.
The Holy Spirit is the Spirit of Truth and if you are lying to yourself, or even not admitting the whole truth to yourself, you will find that all the praying in the world will not help you. Your self-deceit is also an attempt to deceive God, by pretending nothing is really wrong.
Confession is one of the most important acts of a Christian:
I acknowledged my sin unto thee, and mine iniquity have I not hid. I said, I will confess my transgressions unto the Lord; and thou forgavest the iniquity of my sin. Ps. 32:5
He that covereth his sins shall not prosper: but whoso confesseth and forsaketh them shall have mercy. Prov. 28:13
If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.1 John 1:9
Above all else, honesty to God and one's self is key in battling sin and growing as a Christian.
