How do you know you are loved by somebody?

In the letter to the Ephesisans, Paul longs for them to know this love which surpasses knowledge. How can we know something if it surpasses knowledge?

The love we have for our children or parents can be beyond our ability to express or explain and, yet, we know we are loved or that we love.

The measurement of God's love is beyond our understanding but we can still know, deep within our hearts, that we are loved by Him.