A fifth part - Better than the margin. The meaning seems to be that the lintel was one-fifth of the width of the wall, and each door-post one-fifth of its height. Thus the opening was a square of four cubits, or of six feet.

And for the entering of the oracle he made doors of olive tree,.... The door of the holy of holies was a two leaved or folding door, made of olive wood; typical of Christ, the door into the church above and below, the way to heaven and eternal life, the true olive tree:
the lintel and side posts were a fifth part of the wall; four cubits, twenty cubits being the breadth of the oracle; or the lintel was four cubits, twenty being the height of it also, 1-Kings 6:20.

for the entering of the oracle--The door of the most holy place was made of solid olive tree and adorned with figures. The door of the holy place was made of cypress wood, the sides being of olive wood.

Fifth part - That is, four cubits in height or breadth, whereas the wall was twenty cubits.