And to know the love of Christ, which passeth knowledge, that ye might be filled with all the fulness of God.
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." It is a verb expressing experiential knowledge. The Greek word that was translated "knowledge" here was "GNOSIS," a noun denoting the act of knowledge. Simply put, Paul was praying that we would experience the love of God that 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) 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 (1Jo 4:8).
Since a true revelation of God's love makes us full with the fullness of God, then not being full of God must mean there is a lack of understanding and experiencing God's love.