Adam Clarke on Psalms 78:35

That God was their rock - They recollected in their affliction that Jehovah was their Creator, and their Father; the Rock, the Source, not only of their being, but of all their blessings; or, that he was their sole Protector.

And the high God their Redeemer - ואל עליון גאלם veel elyon goalam, "And the strong God the Most High, their kinsman." That one who possessed the right of redemption; the nearest akin to him who had forfeited his inheritance; so the word originally means, and hence it is often used for a redeemer. The Hebrew word גאל goel answers to the Greek σωτηρ, a savior; and is given to the Lord Jesus Christ, the strong God, the Most High, the Redeemer of a lost world. After this verse there is the following Masoretic note: חצי הספר chatsi hassepher, "The middle of the book." And thus the reader has arrived at the middle of the Psalter, a book for excellence unparalleled.