Here we move from inanimate objects and lower life forms in our world to real people. These verses are asking all people to learn to appreciate the God who created our world. The list of people in verses 11-12 represents a descending social status. Perhaps religious people are not mentioned as they are the ones calling all others to praise God.
Obviously, there are more people who do not appreciate God than do appreciate Him. These verses are not a demand, but a request. Think of the exhortation this way, ‘Don't you people realize that God created all of this? Instead of complaining about how bad life is, appreciate all that He has done for us. After all, we will live with Him forever if we choose to, and we should praise Him for the world around us and for the lives He has given us.’
These verses are a plea for us to spread the word about Him to others. It is about asking others to join us in honoring Him as the God with our lives.
 He also exalteth the horn of His people, the praise of all His saints; even of the children of Israel, a people near unto Him. Praise ye the LORD.
The final verse of this Psalm focuses on believers themselves. The writer is encouraging us to praise Him in effect, even if no one else wants to join us.
What is the “horn” a reference to in this text? For animals, a horn is their main source of strength. The point that must be observed is that it is God who strengthens us (that is, gives us the power) in order that we spread the word about Him to others. Now notice that the “horn” is something God raises up for His people. This is probably a reference to the Messiah, (Jesus) who is to come into this world. After all, remember this Psalm was written before Jesus’ first advent.
For children of God today, we must be busy to tell the world about Christ. His love to us is reason alone that should praise Him. As we praise Him and share of His love for people, then they will have opportunity to learn God loves them.