Or HaChaim on Deuteronomy 31:8/אור החיים על דברים ל״א:ח׳

1 וה׳ הוא ההולך לפניך, "as to the Lord, it is He Who will walk in front of you." In this instance Moses did not refer to the Lord as "your G'd" as he did on most other occasions. The reason is that G'd does not associate His name with individuals who are still alive. When speaking of the Jewish people as a whole it is quite in order to refer to G'd as "your G'd" such as in Exodus 20,2 "I am the Lord your G'd," the opening sentence of the Ten Commandments.

2When Moses refers to G'd by the pronoun הוא, saying "He walks before you," instead of saying "and G'd walks before you," he did so to preclude us from thinking that G'd plus some other force would destroy the Canaanites. Omission of the word הוא would have left us with והשם, "and G'd, etc." Moses did not want that anybody should misunderstand the meaning of the letter ו in this context.

3הוא יהיה עמך, "He will be with you." Moses again stresses the הוא, to emphasise that G'd's שכינה i.e. a very high level manifestation of His presence will walk in front of Joshua. הוא יהיה עמך, this manifestation of G'd's presence will remain at Joshua's side. Its effect will be that Joshua will not weaken in face of a variety of challenges.