Why do we say that God is unchanging? Because He is perfect and thus He can neither improve nor decline. Our reading today (Psalms 96-102) proclaims His eternal, perfect existence. In Him we are secure. All that He has made is wonderful but He is the One to whom we owe our worship and in whom we trust.
Let His praise be in your mouth and heart.
[For more reflections on this passage see the corresponding reading in my book Cover to Cover: Through the Bible in 365 days].