John Gill Commentary Psalms 56:10

"In God (I will praise [his] word), In Jehovah (I will praise [his] word)," — Psalms 56:10 (ASV)

In God will I praise [his] word
These words are repeated from (Psalms 56:4); and for the greater certainty of the thing, and to show his fixed resolution to do it, and his strong affection for the Lord and his word, they are doubled;

in the Lord will I praise [his] word :
in the former clause the word "Elohim" is made use of, which, the Jews say, denotes the property of justice, and in the latter Jehovah, which with them is the property of mercy; and accordingly the Targum paraphrases the words,

``in the attribute of the justice of God will I praise his word; in the attribute of the mercies of Jehovah will I praise his word;'' and to the same sense Jarchi: that is, whether I am in adversity or prosperity, receive evil or good things from the hand of the Lord; yet will I praise him: I will sing of mercy and of judgment, (Psalms 101:1); or rather the one may denote the grace and goodness of a covenant God in making promises, and the other his truth and faithfulness in keeping them; on account of both which he is worthy of praise. The word "his" is not in either clause in the original text, and they may be rendered, "in God will I praise the word; in the Lord will I praise the word": in and by the help, assistance, and grace of Jehovah the Father, will I praise the eternal and essential Word, his Son. The Targum renders it his "Memra"; a word often used in it for a divine Person, the eternal Logos; the loveliness of his person, the love of his heart to his people, the fulness of grace that is in him, the offices he sustains on their account, and the virtue of his blood, righteousness, and sacrifice, render him praiseworthy in their esteem.