Though you do not know him, I know him. If I said I did not, I would be a liar like you, but I do know him and obey his word.
NIV
Yet you do not know Him or recognize Him and are not acquainted with Him, but I know Him. If I should say that I do not know Him, I would be a liar like you. But I know Him and keep His word [obey His teachings, am faithful to His message].
AMP
Yet ye have not known him; but I know him: and if I should say, I know him not, I shall be a liar like unto you: but I know him, and keep his saying.
KJV