Exodus 20

 I always thought the reasoning of the commandment to honor parents was interesting - 

"Honour thy father and thy mother: that thy days may be long upon the land which the Lord thy God giveth thee."  (Exodus 20:12)

The promise of obedience was to the child.  I like the explanation of David R. Ridges - 

"The implication in the wording of this commandment is that if children do not bring honor to their parents and family, they will not last long in the promised land. This was indeed the case. It was only through the righteousness of the people that the Holy Land would remain theirs. When they turned to wickedness, they were no longer honoring their parents and were subsequently carried away captive and scattered by enemy nations. In a symbolic sense, if we have righteous parents and do not honor their righteous traditions and teachings, we will be drifting away from the standards of the gospel and thus will not remain in the land (the kingdom of God). 

Some children have a problem when it comes to keeping this commandment. How does one honor dishonorable parents? Perhaps the simplest answer is to differentiate between obeying and honoring, if the situation demands it. The best way to bring honor to our parents is to live honorably, even if it goes contrary to their desires for us. Obeying dishonorable requests, traditions, examples, and so forth is not what this commandment requires and does not bring honor to parents."  (Ridges, David J.. The Old Testament Made Easier - Part 2 (Kindle Locations 2012-2020). Cedar Fort, Inc.. Kindle Edition.)