The prophet Malachi received the following in his oracle from the LORD:
A son honors his father, and servants their master. If then I am a father, where is the honor due me? And if I am a master, where is the respect due me? says the LORD of hosts to you, O priests, who despite my name (Mal 1.6).
One of the more impressive points of Christian theology is that it teaches everyone to pray to God as Father. Thus we were taught by Jesus to pray: Our Father who art in heaven (Mt 6.9-13). This is important because it means we are not left as orphans in the world; we have a heavenly Father who cares for us and takes care of our needs, to whom we are taught to pray every day for our bodily needs. The doctrine of the Fatherhood of God is also a comfort to us when we sin, because we know that God, as our Father, forgives us.
At the same time, it seems that this paternal relationship can be abused. Some persons take advantage of their parents, assuming goodwill to the point of disregarding the parent as a person with rights and dignity of her own. Evidently this had been happening among the people of God, because he has to remind them of basic social norms vis-a-vis the relation of children to parents. Children respect and honor parents; that is what parents expect, and that is what God commands them as well (Exod 20.12). How much more, then, ought we to respect and honor God, who is a father to us beyond what any earthly father can be?
Likewise with the master-servant relation. In a more contemporary vernacular, those in positions of authority expect to be respected by those who are under them, especially from employees. A boss expects that his employees will respect him, and if you want to keep your job for some amount of time, you will respect your boss. How much more should we respect God whom we call "the LORD"? If he is a LORD, he ought to be respected as such. Otherwise our divine titles are empty phrases.
Some persons may ask the question: why does God care so much about being honored? He seems kind of needy. I think this objection is immature, however. Honor is an important part of being a healthy, balanced person. It means recognizing value and respecting it, properly orienting yourself to what is good without expecting anything in return. It is a way of escaping the economics of our ordinary relations -- do ut des, you scratch my back, etc. -- and recognizing that the world is bigger and greater than what it can do for me. There are things to which I must stand under and submit and honor; it is a way of recognizing that I am not the center of the universe.
This evidently was an especially important lesson for priests to learn. Here I think we have some fine points of teaching for those such as myself who are interested in ministry. The priest, as a sort of representative of God to the people and of the people to God, ought especially to embody the proper respect and honor for God. The LORD said through Malachi that these priests "despised his name" or his reputation; this means that they didn't take care to approach God with the proper respect due to him and with a proper attention to his reputation.
I've said in other contexts that we as Christians inevitably become representatives and ambassadors of God to the non-Christian world. This is doubly true for those in positions of authority and ministry, such as pastors and priests. They have to pay special attention to themselves and the ways they represent God to others. This is why stories of sex scandals involving pastors or priests are so troubling; the very persons whom we expect to be near to God and to have dedicated their lives to God go off and do things even "ordinary" persons would never do.