Looking Through A Glass Darkly

The reference is probably to the difficulty seeing clearly, with yourself or someone else.  In context, it probably means we don’t really know what’s going on with someone claiming to have a spiritual gift like “tongues” and therefore — the MAIN THING is to behave with agape’.  

Think of all the people you meet whose inner life, motives, hurts, broken relationships, satisfying relationships, pressures, illnesses, fear and hopes and stuckness you do not know.  Talk about looking through a glass darkly (I Corinthians 13:12)  The more excellent way, the harder, more rarified “way over a high mountain pass” is that of agape’.  

For the person of faith, the way of agape’ combines well with the inevitable lack of clear vision we have.