This is how we know that we know him: if we keep his commandments.
Wuest comments: "We do know" is ginosko, ’to know by experience’ as contrasted to oida, ’absolute, immediate knowledge of a fact once for all" (112). Vine says that the word "frequently indicates a relation between the person knowing and the object known..." (298). Intimacy is also involved in this knowledge. This kind of relationship is what fellowship with God is all about. It is to know Him in a very intimate and experiential manner and to enjoy a very close relationship with Him. Intellectual awareness and academic understanding are definitely involved, but this knowledge goes far beyond these feats of the mind. To know the Lord intimately, one must both learn about Him and learn Him. It is a relationship that involves participation in thought and activity. The Gnostics claimed to have this knowledge, but did they really have this close, intimate relationship with the Lord? Their actions proved otherwise. John uses the expression, "we do know that we know him" eight times in this epistle, signifying the certainty we can have in Christ. "I know that I know God" is a strong statement. To know something is one thing, but to know that we know something expresses an assurance unsurpassed. Far too many Christians speak with doubt about their salvation or their relationship to God with such expressions as "I hope I am saved" or "I hope I get to go to heaven." Such is not the tenor of scripture. John says, "I know that I know," showing an assurance of his position before God. Hope is not desire alone; it consists of both desire and expectation. Christians should testify to their fellowship with God with a language of true hope. (Compare 2 Timothy 1:12; 2 Timothy 4:8; 2 Corinthians 5:1.)