a pure heart

"See now that ye love one another" (1 Peter 1:22). Obviously, this love is not a wild plant that will grow of itself. It is there in the heart by a divine planting, but it must be cultivated... The human heart must be cultivated; we must work on it. We must pray, search the Word, obey, believe and humble ourselves, opening our minds to the incoming Holy Ghost so that we might cultivate and see that we love one another.

How? "With a pure heart." No other kind of heart can love purely; because for the heart to love purely it must love unselfishly. Unselfish love does not exploit its object and it does not ask anything in return. That is so lofty that the modern world knows little or nothing about it.

This true love is to be demonstrated "fervently." God hates everything that is halfway. He hates half-minded people... "A double minded man is unstable in all his ways" (Jas 1:8)...

Then Peter talks about being lukewarm. Is a bottle half full of something or half empty? Is lukewarm water half warm or half cold? Is a half Christian a half sinner and half Christian? I do not know, but I do know this: God will sweep the whole business out together. He will have nothing to do with half stuff. Did He say we are to be full unto the half fullness of God? Never. For God to say a thing like that, He would not be God. Filled unto the fullness of God, He said, not unto the half fullness. God has nothing to do with half-full things. He gives us a whole day, not a half day; He gives us a whole personality, not a half personality; a whole mind, not a half mind; a whole salvation, not a half salvation. And He expects our love to be a whole love, fervent and not half cold. "So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth" (Rev. 3:16).

Think it over. See that you have purified your soul by believing the truth through the Spirit unto one thing, love of the brethren. See to it that love goes to work and you really do love each other fervently out of a pure heart.

(A.W. Tozer, Living As A Christian -- Teachings from First Peter)