The clear command of Psalm 148 is that all of creation should praise the Lord.
Three reasons are given why in verses 5 & 6. They say:
5 Let them praise the name of the Lord,
For He commanded and they were created.
6 He also established them forever and ever;
He made a decree which shall not pass away.
The first reason is stated in the second half of verse 5, because He created everything.
The second reason in the first half of verse 6, because God sustains everything. Everything was not only initiated, created by God but only continues to exist because of Him.
The third reason is stated in the second half of verse 6, because He has decreed everything. God has decided and ordered where in creation everything should exist, how long it should exist and how it should function. Everything in creation owes its ability to do what it does to God.
Then in verse 9 reference is made to one of the main ways creation praises God. It speaks of ” fruitful trees “. When fruit trees are fruitful they praise God. When anything in creation does what it was created to do, when it bears fruit, functions in whatever way it is meant to, it expresses praise to God.
When we, man, the pinnacle of God’s creation bear fruit we expresses praise to God. The fruit of the Spirit and the fruit of all good deeds, Christ likeness & God’s works expressing themselves through us.
These express praise to God, they magnify, draw attention to Him, because whenever something created or invented operates as it was designed to it draws attention and gives glory to the creator, inventor.
From this psalm remember the three reasons why we praise God ( verses 5 & 6 ) and how we praise God alluded to in verse 9.