I am the Lord, your God, who rescued you from the land of Egypt and from the house of slavery. You shall have no other gods before my face.
The first part of this commandment is like a preface to the whole Law. For, when He affirms that He is the Lord, our God, God declares Himself to be the one who has the right to command, and to whose commandment obedience is due. So it is that He says through His prophet: “If I am a Father, where is the love (which is due to Me)? If I am Lord, where is the reverential fear (which is due to Me)?” Malachi 1:6
In a similar way He reminds us of His blessings, making it obvious how ungrateful we are if we do not obey His voice. For it is by the same goodness through which He rescued the Jewish people from the slavery of Egypt that He also delivers all His servants from the Egypt which continuers to exist, that is, from the power of sin.
His prohibition of having other gods means that we must not attribute anything which is proper to God to any other being at all.
And He adds before My face, declaring in this way that He wishes to be acknowledged as God, not just by an outward confession, but in pure truth from the depth of the heart.
Now, these are the things which are proper to God alone and which cannot be transferred to another without robbing Him; that we should worship only Him, that we should rely on Him with our whole trust and with our whole hope, that we should acknowledge that it is from Him that whatever is good and holy comes, and that we should praise Him for all goodness and holiness.
John Calvin, Truth For All Time, pp. 11, 12