There can be no doubt as to the significance of this primary number. In all languages it is the symbol of unity. As a cardinal number it denotes unity; as an ordinal it denotes primacy. Unity being indivisible, and not made up of other numbers, is therefore independent of all others, and is the source of all others. So with the Deity. The great First Cause is independent of all. All stand in need of Him, and He needs no assistance from any.
“One” excludes all difference, for there is no second with which it can either harmonize or conflict.
When it is written: “Hear, O Israel, the Lord thy God is one Lord,” it does not deny the Doctrine of the Trinity, but it excludes absolutely another Lord: it excludes, therefore, all idolatry.
Hence the First Commandment declares “Thou shalt have no other Gods” (Exodus 20:3).
It asserts that there is in God a sufficiency which needs no other; and an independence which admits no other.
It marks the beginning. "In the beginning GOD". All our words and works are characterized by the first words of the Bible: “In the beginning God.” Nothing is right that does not begin with Him. “God first” is the voice of Scripture.
“Seek ye first the kingdom of God and His righteousness; and all these things shall be added unto you” (Matthew 6:33) is the testimony of Christ.
“God first” is the great proclamation. The angels sang: “Glory to God in the highest.” This was the beginning of their song. And it was after this that they sang of “good-will” towards man.
Ethelbert W. Bullinger, Number in Scripture (Redding, CA: Pleasant Places Press, 2004), 50.
The first words of Jesus are :
Luke 2:49 (D-R)
49 And he said to them: How is it that you sought me? Did you not know that I must be about my father’s business?