In constructing a stone building, a cornerstone is a main support element where two walls intersect. It was critical to select a quality stone because if the cornerstone would crack, break, or crumble, a major section of the structure would be at risk and likely fall.
As such, usage of the word cornerstone has come to reference anything that is indispensable or critical.
Get Instant Access!
Sign up for Peter DeHaan's newsletter and get weekly info to guide you into a fresh, new faith--from a biblical perspective.