Paul isn't speaking of "cleansing yourself of sin" as Mikko implied. That is impossible. Only Christ can do that, and as I said, He's already done it, on the cross.
The cross is the means by which we can be cleansed if we approach God with a true heart in repentance and faith.
Peter wrote...
1Pe 1:22 Seeing ye have purified your souls in obeying the truth through the Spirit unto unfeigned love of the brethren, see that ye love one another with a pure heart fervently:
1Pe 1:23 Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever.
A Christian has purified themselves through obedience to the truth, a truth revealed through the Spirit, the result being unfeigned love out of a pure heart.
God has given us all things that pertain to life and godliness that HAVING ESCAPED the corruption that is in the world through lust we may be partakers in the divine nature. The result of partaking in the divine nature is love out of a pure heart.
2Pe 1:3 According as his divine power hath given unto us all things that pertain unto life and godliness, through the knowledge of him that hath called us to glory and virtue:
2Pe 1:4 Whereby are given unto us exceeding great and precious promises: that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust.
This deception of a "provisional salvation" which somehow someone receives because they "trust in Jesus" is totally devoid of any dynamic which produces purity of heart. People purportedly saved under this lie remain in a corrupted and inwardly wicked state. The salvation they believe in is imaginary and that is why not a single one of them have any testimony of their hearts having been purified by faith. None of these people have any testimony of laying aside all filthiness and superfluity of naughtiness and receiving the implanted word and thus being a hearer and doer of the word.