The Psalmist tells us those who trust in God will praise Him. Verses 11 and 12 give us the "how and why". Verse 11 states that people will tell others of the benefits of trusting in Him. Verse 12 explains the purpose of passing on knowledge about God: So that all men (and women) may know of His existence and power.
One day all people will praise God. This truth is declared in various places in the Bible. There will come a day, either by free will or by force, that all people will acknowledge the God that created this world (see Romans 14:11 and Philippians 2:10). This is in effect the point of these verses.
 Thy kingdom is an everlasting kingdom, and thy dominion endureth throughout all generations.
Remember that David is using this Psalm to explain reasons why all people should praise God. One of the big picture things to see from reading this Psalm is that God does great things for the whole world in that He makes it possible for all of us to live on earth. However, for those of us who are willing to submit to His eternal payment for our sins, He has blessings that extend to eternity. God is faithful and worthy of our trust.