So...discernment. Here's what +John Cassian had to say to his monks:
"It is discernment which in Scripture is described as they eye and the lamp of the body. This is what the Saviour says, 'our eye is the light of your body, and if your eye is sound then there is light in your whole body. But if your eye is diseased then your entire body will be in darkness'. This eye sees through all the thoughts and actions of a man, examining and illuminating everything which we must do. And if it is not sound in a man, that is, if it is not fortified by good judgment and by well-founded knowledge, if it is deluded by error and by presumption, this makes for darkness in our entire body. The clear thrust of the mind as well as everything we do will be shadowed and we shall be wrapped in the blindness of sin and the blackness of passion. 'If the light within you is darkness,' says the Saviour, 'what a darkness that will be'. For let no one doubt that our thoughts and our works, which originate from the deliberative processes of discernment, will be caught up in the shadows of sin if ever the good judgment of our heart goes astray or is taken over by the night of ignorance."
Error in belief and presumption can destroy the soul.
The life is in Christ and in Him alone.
It is only by receiving Him personally feeding on Him, the Living Word of God personally, that a man is born again and has the power to become a child of God.
But this too requires Spiritual discernment.
Further I testify that nothing can happen in the life of such a Christian without it also happening to Christ. Demons cannot invade Christ and nothing can happen to such a one except either according to Gods will or by His permission.
The short version for those with ears to hear:
In the beginning was the Word, and the Word was with God, and the Word was God. The same was in the beginning with God. All things were made by him; and without him was not any thing made that was made. In him was life; and the life was the light of men. John 1:1-4
But as many as received him, to them gave he power to become the sons of God, [even] to them that believe on his name: Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God. John 1:12-13
But he answered and said, It is written, Man shall not live by bread alone, but by every word that proceedeth out of the mouth of God. Matt 4:4
And Jesus said unto them, I am the bread of life: he that cometh to me shall never hunger; and he that believeth on me shall never thirst. John 6:35
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
Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and [of] the Spirit, he cannot enter into the kingdom of God. That which is born of the flesh is flesh; and that which is born of the Spirit is spirit. John 3:5-6
But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his. Romans 8:9
For ye are dead, and your life is hid with Christ in God. - Col 3:3
Submit yourselves therefore to God. Resist the devil, and he will flee from you. James 4:7
And unclean spirits, when they saw him, fell down before him, and cried, saying, Thou art the Son of God. Mark 3:11
Thou believest that there is one God; thou doest well: the devils also believe, and tremble. James 2:19
And I saw a great white throne, and him that sat on it, from whose face the earth and the heaven fled away; and there was found no place for them. Rev 20:11
Ye are of God, little children, and have overcome them: because greater is he that is in you, than he that is in the world. 1 John 4:4
My sheep hear my voice, and I know them, and they follow me: - John 10:27