The interpretation timeline
Joshua 1:9 Douay-Rheims

Behold I command thee, take courage, and be strong. Fear not and be not dismayed: because the Lord thy God is with thee in all things whatsoever thou shalt go to.

1105 – 1875 3 witnesses

Scholastic

c. 1100 – 1500
1105
A.D.
Rashi Jewish
1040–1105
“I have already commanded you to be stong and courageous. This was said in reference to actual war, as it is said: ‘Have no fear or trepidation.’ Where was he commanded this? He was so commanded in the time of Moshe, as it is said: ‘and command Yehoshua son of Nun etc.’”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“Have not I commanded thee?.... The above things, to go over Jordan with the people into the land of Canaan, and to observe the law of Moses in all things, and to be of good courage, which is again repeated; consider who it is that has given these orders and instructions, the great Jehovah, the everlasting I AM, who is faithful to his promises, and able to perform. The consideration of which would serve to animate him to the work he was called unto, to encourage his faith in God, to engage in his service cheerfully and readily: be strong, and of a good courage; See Gill on Jos 1:6; See Gill on Jos 1:7. be not afraid, nor be thou dismayed; at his enemies, numerous and powerful, nor discouraged at anything in himself, any unfitness for such service, as he might think, or at any difficulties he might fear from the people he had the government of, and was to lead on; it was enough that the divine Presence was promised him, and which is repeated: for the Lord thy God is with thee whithersoever thou goest: or, as the Targum of Jonathan,"for thy help is the Word of the Lord thy God;''See Gill on Jos 1:5.”
Source
1875
A.D.
Keil & Delitzsch Lutheran
1861–1875
“In conclusion, the Lord not only repeats His exhortation to firmness, but the promise that He gave in Jos 1:5 and Jos 1:6. "Have I not" (nonne) is a rhetorical mode of saying, "Behold, I have," the assurance being clothed in the form of an affirmative question. On the words "be not afraid," etc., see Deu 31:6 and Deu 31:8.”
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.