1 John 3:3

And everyone that hath this hope set on him purifieth himself, even as he is pure.

And everyone that hath this hope set on him ... The RSV is a better translation: "Everyone who thus hopes in him." This means, "everyone who hopes in Christ." The great obligation of every person "in Christ" is to exhibit the righteousness and purity so perfectly exemplified in him.

There is another glimpse in this of the "perfection" that God requires of his children. Being as pure as Christ is pure is the same as being "perfect, as your Father in heaven is perfect" (Matthew 5:48), or being "holy, for I am holy" (1 Peter 1:15,16). This idea, or goal, of absolute perfection is unattainable in human strength; but it is achieved for Christians and ascribed to them by reason of their having denied themselves, being baptized "into Christ," and thus made partakers of his sinless perfection. People are saved, not in their own identity, but "as Christ," and "in Christ." This points up the great importance of the expression "in him" as used in this verse (RSV). This should not take away from the power of the exhortation that all Christians should strive to achieve and maintain the very highest state of purity and perfection of which they are capable. Sin can never be any casual business with the Christian.