Keluaran 25:15-16

25:15 The poles must remain in the rings of the ark; they must not be removed from it. 25:16 You are to put into the ark the testimony ¹  that I will give to you.

Keluaran 30:19

30:19 and Aaron and his sons must wash their hands and their feet from it. ² 

[25:16]  ¹ sn The “testimony” is the Decalogue (Exod 24:12; 31:18; Deut 4:13; 9:9; 1 Kgs 8:9); the word identifies it as the witness or affirmation of God’s commandments belonging to his covenant with Israel. It expressed God’s will and man’s duty. In other cultures important documents were put at the feet of the gods in the temples.

[30:19]  ² tn That is, from water from it.