How We Know - Ephesians 3:19

Ephesians 3:19 ESV 

and to know the love of Christ that surpasses knowledge, that you may be filled with all the fullness of God.

Can we know something that surpasses knowledge?

The fullness of God is pleased to dwell in Christ. He allows us to be filled with that fullness, for He is with us and dwells within us. 

We know because He told us so. We know because the Spirit testifies to our spirit that this is so. 

We know because He promised to not leave us alone and God keeps His promises. 

We know something that surpasses knowledge. We speak of faith which bridges the gap between the finite and the infinite. That is how we know.