C. F. Keil and Franz Delitzsch on Exodus 20:3

Exo 20:3

The First Word. - “Let there not be to thee (thou shalt have no) other gods פּני על פּן,” lit., beyond Me (על as in Gen 48:22; Psa 16:2), or in addition to Me (על as in Gen 31:50; Deu 19:9), equivalent to πλὴν ἐμοῦ (lxx), “by the side of Me” (Luther). “Before Me,” coram me (Vulg., etc.), is incorrect; also against Me, in opposition to Me. (On פּני see Exo 33:14.) The singular יהיה does not require that we should regard Elohim as an abstract noun in the sense of Deity; and the plural אחרים would not suit this rendering (see Gen 1:14). The sentence is quite a general one, and not only prohibits polytheism and idolatry, the worship of idols in thought, word, and deed (cf. Deu 8:11, Deu 8:17, Deu 8:19), but also commands the fear, love, and worship of God the Lord (cf. Deu 6:5, Deu 6:13, Deu 6:17; Deu 10:12, Deu 10:20). Nearly all the commandments are couched in the negative form of prohibition, because they presuppose the existence of sin and evil desires in the human heart.