Midrasch zu Schemot 25:15

Why was the acacia-wood placed in between? Because the Torah is called the tree of life, as it is said: She is a tree of life to them that lay hold upon her (Prov. 3:18). He overlaid it with pure gold (Exod. 37:2). Because the words of the Torah are more precious than gold, yea, than fine gold, as is said: More to be desired are they than gold, yea, than much fine gold (Ps. 19:11). And thou shalt make staves of acacia-wood wherewith to bear the ark (Exod. 25:15). They bore the ark with them, and it bore away the sins of Israel, for the Torah within it carries away the sins of Israel.¹²The Hebrew word nasa’ means both “to bear” “to forgive.”