Charles Ellicott Commentary Exodus 25:10

"And they shall make an ark of acacia wood: two cubits and a half shall be the length thereof, and a cubit and a half the breadth thereof, and a cubit and a half the height thereof." — Exodus 25:10 (ASV)

THE ARK.

They shall make an ark. — Arôn, the word here rendered “ark,” is an entirely different word from that previously so translated in Genesis 6:14; Exodus 2:3, which is tebah. Arôn is properly a chest or coffer of small dimensions, used to contain money or other valuables (2 Kings 12:9–10; 2 Chronicles 25:8–11, and other passages). In one place it is applied to a mummy-case (Genesis 1:26). Here it designates a wooden chest three feet nine inches long, two feet three inches broad, and two feet three inches deep.

The primary object of the ark was to contain the two tables of stone, written with the finger of God, which Moses was to receive before he came down from the mount. (See Exodus 24:12, and compare with Exodus 20:16.) Sacred coffers were important parts of the furniture of temples in Egypt. They usually contained the image or emblem of some deity, and were constructed so as to be readily carried in processions.