This beloved Psalm is attributed to David. The chapter begins with the same expression used to end this Psalm. The expression is used in the next Psalm as well. This Psalm will in effect state many reasons why we should praise God. Verse 1 gives us the command to do so. Why? If for no other reason than the fact that He is God and we are not. Another big reason is that it benefits our life here and now by praising Him. I have learned that my life goes better when I make the time to praise Him.
It is important to state here again that the word "LORD" is the most holy name of God. In fact, many religious Jews will not even write out the word "Jehovah" or even the word "God" as they believe it is too holy to be written out.
I am convinced that the "how" we praise God is not as important as the fact we do so in the first place. Don’t get me wrong: The "how" includes the idea of honoring Him as God and respecting who He is and what He has done for our lives. My point is that I am convinced God is interested in us making the effort in the first place to honor Him, and then I have found that He does guide us through His Word as to how He desires to be worshipped.
 Bless the LORD, O my soul, and forget not all His benefits:
 Who forgiveth all thine iniquities; Who healeth all thy diseases;
Verses 2 through 5 are all part of one sentence. If you wonder why we should praise God, some specific reasons are given in these four verses. We ought not to forget all the benefits of being alive and the fact we get to live forever with God. What are those benefits? That is what the next three verses discuss.
The first benefit stated here is that God does forgive all of our sins. Remember that God does not just forgive our sins because He can. God forgives them because we trust in His Son as complete payment of those sins.
When we take the time to become aware of our sins, we should confess them as to say, "Dear God I realize at this moment, You were right and I was wrong on that specific issue". This will draw us closer to God and is also a form of praise.
Let me also discuss the phrase "who healeth all thy diseases". Exodus 15:26 exhorted the children of Israel to listen to the voice of God and do what is right and God would protect them from diseases as He is the LORD that heals. Yes, there is a time in which we ought to take medicine as needed and try to eat right, but one should never ignore that our health requires trust in Him. After all, it is God who brings the healing in our lives. I'll expand on this concept in a moment.