From Ohr Avigdor Shaar Bechinah by Rabbi Avigdor Miller
"And so, when we study the miracles of Hashem in the body we have to begin by realizing that the hand of Hashem is everywhere. In effect we are looking at nothing but the hand of Hashem. We must realize that secular society and what they say are all false. They are wicked liars who are trying their best to conceal the truth of Hashem from the world. But what they are doing is so foolish.
We see the open demonstrations of Hashem’s deeds everywhere, as it says, “All your works praise You, Hashem ... [Their mere existence calls out His praise for they demonstrate His wisdom and His kindness. And it’s all for the purpose of ... ] to make known to man His mighty deeds“ (Tehillim 145:10–12).
The body is a subject about which your thoughts can sing
We have to be strong to turn our backs on the wicked propaganda to which we are exposed, and utilize what Hashem gave us to recognize Him, to admire Him, and to thank Him for His creations. David Hamelech said, “... my thoughts and my body sing to Hashem.“ He did not intend this to be just a poetic expression. He really wanted to say that his thoughts and his body sing to Hashem. Now, it is fairly easy to understand how the thoughts can be singing to Hashem.
But how does the body sing to Hashem? The answer is that although it is the thoughts that can actually sing to Hashem, the body is a subject about which his thoughts can sing. There are various other ideas about which we sing to Hashem, such as that He chose us from all the nations and that He rescued us from all our enemies. These are subjects that have nothing to do with our bodies. But when David Hamelech said “my thoughts and my body,“ he told us that a big part of his thoughts have to do with his body. It is in that sense that the body sings. Therefore, if a person never thinks about the body details that he has to sing about, his prayer to Hashem is nothing but insincere words.
Therefore, in order for us to fulfill the great function of the body, we have to know that the most important function of the body is not merely to help us exist in This World. Rather, it’s like all other things in This World whose function is for the purpose of teaching us about the Creator. That’s what everything in the world is for. So, for example, the sun is supremely important for the world; its real purpose is for mankind to recognize the Creator.