See EGW comment on 1 Peter 1:22; Revelation 7:2, 3.

 “And every man that hath this hope in him purifieth himself, even as he is pure.”
 Does this text mean that the human agent can remove one stain of sin from his soul? No. Then what does it mean to purify himself? It means to look upon the Lord’s great moral standard of righteousness, the holy law of God, and see that he is a sinner in the light of that law. “Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law. And ye know that he was manifested to take away our sins; and in him is no sin.”
 It is through faith in Jesus Christ that the truth is accepted in the heart, and the human agent is purified and cleansed.... He has an abiding principle in the soul, that enables him to overcome temptation. “Whosoever abideth in him sinneth not.” God has power to keep the soul that is in Christ who is under temptation....
 A mere profession of godliness is worthless. It is he that abideth in Christ that is a Christian.... Unless the mind of God becomes the mind of men, every effort to purify himself will be useless; for it is impossible to elevate man except through a knowledge of God. The outward gloss may be put on, and men may be as were the Pharisees whom Jesus describes as “whited sepulchres” full of corruption and dead men’s bones. But all the deformity of the soul is open to Him who judgeth righteously, and unless the truth is planted in the heart, it cannot control the life. Cleansing the outside of the cup will never make the vessel pure within. A nominal acceptance of truth is good as far as it goes, and the ability to give a reason for our faith is a good accomplishment, but if the truth does not go deeper than this, the soul will never be saved. The heart must be purified from all moral defilement (Letter 13, 1893).