The moral philosophy of Jesus
In virtue ethics, the most important thing regarding knowing what's good is what a really virtuous person says. If you want to know what the right thing is, ask the person you know who's the most upright, virtuous person you can find. You shouldn't ask an evildoer whether it is right to do X or Y. Morality is so complicated that this is the best way of figuring out moral issues. You can't hope to figure out morality like 2 + 2 = 4. Morality is a very complicated, tricky thing, and another approach won't really work.
When Jesus is tempted by Satan in the Gospel of Matthew, he gives a very interesting reply to the temptation that sort of goes along with Aristotelian virtue ethics:
Matthew 4:8-10 "Again, the devil took him to a very high mountain and showed him all the kingdoms of the world and their splendor. "All this I will give you," he said, "if you will bow down and worship me." Jesus said to him, "Away from me, Satan! For it is written: 'Worship the Lord your God, and serve him only.'"
Combine that with these verses:
John 5:30 "By myself I can do nothing; I judge only as I hear, and my judgment is just, for I seek not to please myself but him who sent me."
Matthew 19:16-17 "Now a man came up to Jesus and asked, "Teacher, what good thing must I do to get eternal life?" "Why do you ask me about what is good?" Jesus replied. "There is only One who is good. If you want to enter life, obey the commandments."
Jesus identifies God as a being who is so good, so wonderfully upright and loving, that in comparison with God, no one else even deserves to be called 'good'.
I think one can see a bit of a connection between these verses...
Think about it like this: suppose you lived in a town and there was someone in the town who was quite unusual. While everyone in the town is a pretty decent person, this person is something more. This person cannot be tempted to do the wrong thing. When this person thinks about moral dilemmas, you know that he/she will give the right answer, because this person always thinks about the right thing in a clear way. It is impossible to tempt this person with an evil thought.
If you wanted wisdom on any ethical decision, you would always go to this person if you lived in the town. Although we usually make pretty good ethical judgements, the only way you could be really sure, the only way you could be 100% positive whether something was the right thing to do, would be to ask the person who cannot give a morally flawed answer. Whereas you, I, and everyone else can be tempted to see things in a selfish way, this special person must by definition see things in the morally correct way.
If you wanted someone to be the ruler over a society, then if possible, you would pick that particular person. While other people might be good rulers out of the goodness of their own hearts, this 'un-temptable' person would be good out of necessity. Surely, picking that person as a ruler could not go very wrong.
If you think about it like this, then it's easy to see the logic of Jesus' answer to Satan in Matthew 4:10. God is someone who cannot be tempted to do the wrong thing (James 1:13; Titus 1:2). So in Jesus' view, if you're in any doubt as to whether you should do something, there is one person who's answer you can always trust (assuming you could actually talk to Him/Her/It). The answer of a God who cannot be tempted by evil is 100% trustworthy by definition, unlike the answer of someone not like that (although someone else's view might be right as well, it is not trustworthy by definition).
So we see that, if you assume that there is a God who is like the person in the town example, and like the God alleged in the Bible, then there is a certain logic to everyone deferring to this God. Everyone else in all of existence can be tempted to do the wrong thing - even the human part of Jesus (Heb 4:15). Even the angels were tempted at one point according to Thomas Aquinas' interpretation of the fall of Satan. But not God - for some reason God, and only God, is impossible to tempt. So assuming that this God existed and this situation was the case, then wouldn't it make sense if everyone listened to what He/She/It had to say? And not only listen, but act accordingly?
If God really cannot be tempted by evil, then serving God like Jesus ("serve Him only") would actually give us our freedom, it wouldn't take it away. A God who couldn't be tempted to do evil would be love. And part of loving people is giving them free will. So we can see that only serving God means being a) free and b) honouring other people's freedom through love.
So if you look at Jesus' views in a 'virtue ethics' way, Jesus essentially says that the person to ask when it comes to moral issues is the only person who can never be tempted. If you follow this person, then the result will never go wrong (assuming you actually knew what God was saying). Given the truth of such a situation, serving this person with 'all your heart, soul, strength and mind' guarantees that the right thing will always be done. Therefore, as Jesus says, you should "serve only" this God rather than yourself or someone else.