God is beyond human comprehension. We cannot begin to even imagine the greatness of an infinitely holy God. We simply need to appreciate His power. We must accept the fact that "He is" even though we can't grasp the size and scope of His power.
 The LORD lifteth up the meek: He casteth the wicked down to the ground.
The Psalmist transitions from calling attention to how big God is, to the fact that He sustains the humble and casts the wicked to the ground (that is, He frustrates their plans). This God is so powerful; He cares about our world and gets involved in our world in order to bring Him glory over time.
To explain it another way, He uses those of us who humble ourselves before Him, whether we realize it or not. If we choose to let God guide our lives, again, He will do so whether we realize it or not.
 Sing unto the LORD with thanksgiving; sing praise upon the harp unto our God:
If God is guiding us, does that mean we ignore our duties and just praise Him all day like this verse suggests? Of course not. The point is we should pause every now and then, and show gratitude to the one (God) who gave us our lives. More importantly, He gave us a purpose for living, which is to bring Him glory through our lives. This is one big reason why we ought to praise Him.
Another reason we praise Him is because when we praise Him, we are then drawing upon His power to make that difference in our world. As we humble ourselves before Him, that realization guides our lives giving us the ability not only to praise Him but also to use our lives to make a difference for Him.
Every Christian should use his talent(s), gift(s) and passion(s) in some way to make a difference for God. If we seek Him through prayer and through His word, God will guide us and teach us how it is we can glorify Him.