For the Lord most high - Yahweh, the Most High God; that is, who is exalted above all other beings. Compare Exodus 18:11; 1 Chronicles 16:25 Psa 96:4; 2 Chronicles 2:5; Psalms 95:3.
Is terrible - literally, is to be feared; that is, reverenced and adored. There is an idea in the words “terrible” and “terror” which is not contained in the original, as if there were something harsh, severe, stern, in his character. The word in the original does not go beyond the notion of inspiring reverence or awe, and is the common word by which the worship of God is designated in the Scriptures. The meaning is, that he is worthy of profound reverence or adoration.
He is a great king over all the earth - He rules the world. He is a universal Sovereign. The immediate “occasion” of saying this, when the psalm was composed, was evidently some victory (which had been achieved over the enemies of the people of God) so decided, and so immediately by the divine power, as to prove that he has absolute control over all nations.