Why do men need to obey God's Laws? The reason is simple, because the world, including men themselves, were created by God. How to create? By operating according to the principles established by God.
There are four seasons in a year, the sun rises every morning, cattle and sheep feed on grass, and fish live in water ..... Each and every species have their own set of rules. If one day the sun decides to rise at night instead of in the morning, wouldn't the world be in chaos?
Romans 1:20 Since the creation of the heavens and the earth, the eternal power and divinity of God has been clearly known, though invisible to the eyes, but through the things that have been made, it is known, so that there is no excuse.
The whole world is actually a very precise, subtle and perfectly formulated structure. All things are inter-related - everything depends on one another for survival, and serves one another in return. Bees disperse pollen for plants, plants produce fruits for human consumption, and humans till the ground and take care of the cattle. Every creature follows the Laws of Nature and does not require any instructions by anyone. Human is the only creation that has been given free will by God. But also because of this, many problems have arisen as a result.
If we take a look through the history in the Bible, for every disaster recorded, was there not a time when some people have violated the Law of God? King David had many wives and concubines, and he even took the wife of a righteous man by force. This eventually led to incest among his children, and they ended up killing each other. King Ahab of Israel did all the evil things, and robbed an innocent man Naboth of his vineyard. His evil works caused many people to suffer, and finally his entire family was destroyed. There are numerous similar examples in the Bible, as the prophet Isaiah said:
Isaiah 53:6 We are all like sheep that have gone astray; each of us has gone his own way...
Just imagine, if everyone in the world obeyed God's Laws by doing justice, showing mercy, and loving their neighbors as themselves, wouldn't this world be a much lovelier place?
Of course, we live in a fallen world, and we cannot expect everyone to obey God's Laws, but I hope as Christians, we should at least make an effort to abide by it. If we believe in Christ, we should believe that His Laws are good. And if we really believe they are good, then how can we not follow them?
James 2:17 So faith without works is dead.