For I know - I, as the representative of Israel, and speaking in the, name of the people. This is said as the foundation or the reason for praise. It was the thorough conviction of the psalmist that God was great above all who were claimed to be gods, and that he only was worthy of worship.
That the Lord is great - See the notes at Psalms 95:3.
And that our Lord is above all gods - All that are worshipped as gods.