"I pray that you, being rooted and established in love, may have power, together with all the saints, to grasp how wide and long and high and deep is the love of Christ," Have you ever heard the VBS song "deep and wide"? It goes like this: "Deep and Wide, Deep and Wide, there's a fountain flowing deep and wide". It's so simple, yet so profound. God's love is a fountain that is flowing deep and wide. It's a flood of grace and a flood of love. Which sounds so very corny, but try to get past that and think about it. In this verse, verse 17-18, Paul tells us that the fountain of his love isn't just deep and wide, it's deep and wide and long and high. It surrounds. "...and to know this love that surpasses knowledge - that you may be filled to the measure of all the fullness of God." So at the beginning of this paragraph we read where Paul said that he prays that we "may have power... to graps... the love of Christ" but here, he says that the "love surpasses all knowledge". God can give us the power to grasp how great his love is, but it surpasses knowledge. We can grasp how "wide and long and high and deep" God's love is, but it surpasses our knowledge. I don't think Paul is talking about a mental 'knowing', I think he's talking about us knowing God's love and understanding that we can never understand it.
"Now to him who is able to do immeasurably more than all we ask or imagine, according to his power that is at work within us, to him be glory in the church and in Christ Jesus throughout generations, for ever and ever! Amen." God can do immeasurably more than all we ask or imagine. Our wildest dreams can't ever compare to what God can do. That's what we're here for. We're here for the glory of Christ Jesus, He who can do immeasurably more than whatever our human hands are capable of. That's where it's at.