The interpretation timeline
Deuteronomy 31:6 Douay-Rheims

Do manfully and be of good heart: fear not, nor be ye dismayed at their sight: for the Lord thy God he himself is thy leader, and will not leave thee nor forsake thee.

A.D. 430 – 1771 3 witnesses

Patristic

before A.D. 750
430
A.D.
Augustine of Hippo Patristic
A.D. 354–430
“Pay attention to what comes next: "Without love, a measure of money is sufficient for present needs, because he himself said, 'I will not forsake you; I will not desert you.' " "You were afraid of all kinds of evils, against which you were saving money; count me as your guarantor." That's what God says to you. God—not a man, not your equal or you yourself—says to you: "I will not forsake you; I will not desert you." If a person made such a promise, you would trust him. God makes it, and you hesitate? He made the promise, put it in writing, made out the bond; you needn't worry at all.”
Source

Scholastic

c. 1100 – 1500
1105
A.D.
Rashi Jewish
1040–1105
לא ירפך means He will give you no looseness that you should be abandoned by Him (cf. Rashi on Deuteronomy 4:31).”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“And Moses called unto Joshua,.... Who might be at some distance from him, with the tribe to which he belonged. The Targum of Jonathan adds,"out of the midst of the people:" and said unto him, in the sight of all Israel; now assembled together, and what follows was said in their hearing, to make him the more respectable to them: be strong and of a good courage; the same that is said to the people in Deu 31:6, and which was still more necessary in him, who was to be their general, and to go at the head of them, and lead them on to battle; and though Joshua was a man of courage and valour, as well as had military skill, as appears by his fight with Amalek, Exo 17:9; yet such an exhortation was not needless, seeing he had so much work to do, and so many enemies to contend with: for thou must go with this people unto the land which the Lord hath sworn unto their fathers to give them, and thou shalt cause them to inherit it; the Targum of Jonathan is,"which the Word of the Lord hath sworn to give;''the land of Canaan, thither he must go with them; this was the will and determination of God, and he must go alone without him, Moses, which would be a trial of his courage.”
Source
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.