Albert Barnes Commentary Exodus 31:18

"And he gave unto Moses, when he had made an end of communing with him upon mount Sinai, the two tables of the testimony, tables of stone, written with the finger of God." — Exodus 31:18 (ASV)

Two tables of testimony - See Exodus 25:16; Exodus 32:15.

The tables of stone which represented the covenant between Yahweh and His people, and which, when covered with the mercy-seat were to give the sanctuary its significance, are now delivered to Moses in accordance with the promise in Exodus 24:12.

The history of what relates to the construction of the sanctuary is here interrupted, and is taken up again in Exodus 35:1.