Which is the First Commandment?

The first commandment is, “You shall have no other God’s before Me.” (Exodus 20:3)

Deuteronomy 6:14-15 (NASB) You shall not follow other gods, any of the gods of the peoples who surround you, for the LORD your God in the midst of you is a jealous God; otherwise the anger of the LORD your God will be kindled against you, and He will wipe you off the face of the earth.

Jeremiah 35:15 (NASB) You shall not follow other gods, any of the gods of the peoples who surround you, for the LORD your God in the midst of you is a jealous God; otherwise the anger of the LORD your God will be kindled against you, and He will wipe you off the face of the earth.

The preface in Exodus 20:2 has already indicated that the Yahweh is their God; therefore, the phrase “before Me” means in my presence. They were not to acknowledge any other so called god or gods except Yahweh. 

The apostle Paul wrote:
1 Corinthians 8:5-6 (NASB) For even if there are so-called gods whether in heaven or on earth, as indeed there are many gods and many lords, yet for us there is but one God, the Father, from whom are all things and we exist for Him; and one Lord, Jesus Christ, by whom are all things, and we exist through Him.

The apostle Paul is portraying both the Father and the Son as one in the since of Deuteronomy 6:4 (NASB).
“Hear, O Israel! The LORD is our God, the LORD is one!