The builders select stones to fit into the wall.  Certain sizes and shapes are selected for this or that spot.  Sometimes a stone that looks as if it would never fit in the building, and has been cast aside, is the very stone needed, the cornerstone.  God is building His temple on Jesus the Cornerstone.  When our building is rightly related to Him as the essential Stone, then the house will stand.

“This Jesus is ‘the stone that was rejected by you, the builders; it has become the cornerstone.’  Acts 4:11 (NRSV)