Adam Clarke on Exodus 32:16

The tables were the work of God - Because such a law could proceed from none but himself; God alone is the fountain and author of Law, of what is right, just, holy, and good. See the meaning of the word Law, Exo 12:49 (note).

The writing was the writing of God - For as he is the sole author of law and justice, so he alone can write them on the heart of man. This is agreeable to the spirit of the new covenant which God had promised to make with men in the latter days: I will make a new covenant with the house of Israel - I will Put My Laws In Their Minds, And Write Them In Their Hearts, Jer 31:33; Heb 8:10; 2Cor 3:3. That the writing of these tables was the writing of God, see proved at the conclusion of the last chapter.