1 John 3:19

KJV

And hereby we know that we are of the truth, and shall assure our hearts before him.

ESV

By this we shall know that we are of the truth and reassure our heart before him;

For context, read the previous verse: My little children, let us not love in word, neither in tongue; but in deed and in truth. (1 John 3:18 KJV) In the KJV, the truth is immediately known (“…hereby we know…”). Modern versions turn this knowledge into a realization made sometime in the future (“…we shall know…”). 

Scripture quotations marked (ESV) are from the ESV® Bible (The Holy Bible, English Standard Version®), © 2001 by Crossway, a publishing ministry of Good News Publishers. ESV Text Edition: 2025. The ESV text may not be quoted in any publication made available to the public by a Creative Commons license. The ESV may not be translated in whole or in part into any other language. Used by permission. All rights reserved. www.esv.org

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