to let go: to release your hold so a person or thing departs, stays behind, or is left where it is
At its root this is a verb of separation. You take your hand off, and what you were holding moves away or stays behind while you go on. The same motion covers:
- a man walking out on a wife
- disciples dropping their nets to follow Jesus
- a traveler simply leaving a town
From that one image the New Testament draws a wide spread of plain uses. A fever "leaves" a sick person. People "leave" boats, families, and houses. A man dies and "leaves" a widow with no children. Not one stone is "left" standing on another. The leaving can be tender ("Peace I leave with you") or severe (a house "left" desolate, a hireling who "leaves" the sheep, the disciples who "left him and fled").
The constant thread is release. Something held, kept, or staying with you is set loose or left where it stands. The forgiveness sense and the permission sense both grow out of this physical letting-go, which is why one Greek verb has to be split into many English words.