Note 13 at Eph. 3:19: How can we know the love of God if it passes knowledge? This sounds like a contradiction.

The Greek word that was translated "know" in this verse is GINOSKO, which is a verb expressing experiential knowledge. The Greek word that was translated "knowledge" here was GNOSIS, which is a noun denoting the act of knowledge. Simply put, Paul is praying that we would experience the love of God which passes mere knowledge about it.

Note 14 at Eph. 3:19: The end result of having understanding and experiential knowledge (see note 13 at this verse, above) of God's love is that we will be filled with all the fullness of God. God's love is the key that opens the door to everything that God is. God is love (1 Jn. 4:8).

Since a true revelation of God's love makes us full with the fullness of God, then a lack of being full of God must mean there is a lack in understanding and experiencing God's love.