What is the purpose of mankind? To give God glory and enjoy Him.
Glory is something we can measure and experience. When you witness something so incredible it will evoke a sense of amazement, respect, fear. God's goal for every action He does is to bring himself glory. The vastness of the universe is to be looked upon with awe and to recognize how glorious God is in His wisdom and power. He saves us, a small speck in the universe, because He loves us and most importantly to give glory to Him.
The reason God chooses His glory over everything is because we must understand that it is the purest and highest level imaginable - it is not of selfish intent as it leads to blessings beyond compare. The more we promote His glory the more benefit we will see for ourselves, this doesn't happen if we are self-centered.
Nature gives God glory passively (just by existing). Humans are to intentionally and actively. To do this we must know and love Him. We know we will never be able to fully comprehend God but this shouldn't stop us from getting to know who He is.
God is the greatest of anything He ever created, therefore we should be giving Him the best we have and are. Whatever we do we must do it for Him not just our own gain and recognition. When we use the gifts and blessings God has given us for His pleasure we will be giving Him glory. We need to trust in Him.