Moses
Deuteronomy 6:4ESV·traditional attribution

“Hear, O Israel: The LORD our God, the LORD is one.

John Calvin Reformed @genevareformer

4. Hear, O Israel. When Moses proclaims that God is One, the statement is not confined to His sole essence, which is incomprehensible, but must be also understood of His power and glory, which had been manifested to the people; as though he had said, that they would be guilty of rebellion unless they abode in the One God, who had laid them under such obligations to Himself.

Matthew Henry Presbyterian @wholebiblehenry

Here is, I. A brief summary of religion, containing the first principles of faith and obedience, Deu 6:4, Deu 6:5. These two verses the Jews reckon one of the choicest portions of scripture: they write it in their phylacteries, and think themselves not only obliged to say it at least twice every day, but very happy in being so obliged, having this saying among them...

Commenting on Deuteronomy 6:4-16

John Gill Reformed Baptist @doctorgill

Hear, O Israel,.... These are the words of Moses, stirring up the people to an attention to what he was about to say of this great and momentous article, the unity of God, to prevent their going into polytheism and idolatry.