Dictionary.com defines "moral" as "of, pertaining to, or concerned with the principles or rules of right conduct or the distinction between right and wrong".
Whenever we look at morality in a forum such as this, it is always helpful to present what is generally known as the "Moral Argument for the Existence of God". Briefly put, if an absolute and moral God does not exist, then objective moral values do not exist. However, objective moral values do exist (in other words, some actions are morally wrong whether someone believes they are wrong or not), and therefore, an absolute and moral God also exists.
Thus, the definition of moral behavior comes directly from God, and moral behavior is nothing other than obedience to His commands.
The question, however, is why should we be moral? Why should we obey God?
The Bible teaches that we are to be moral because obedience to God glorifies He who created us, sustains us, and redeemed us. Obedience is accepted by God as worship (Romans 12:1) and is preferable to Him than sacrifice (Hosea 6:6).
In Matthew 22, when Jesus was asked what the most important of all God's commands was, He answered, "'You shall love the LORD your God with all your heart, with all your soul, and with all your mind'. This is the first and greatest command. And the second is like it: 'You shall love your neighbor as yourself'. On these two commandments hang all the Law and the Prophets."
Based on Christ's words, it has been frequently said that "love" is the greatest command.
According to the Bible, the reason Christians love is because Christ first loved us (1 John 4:19).
He demonstrated His love for us in that, while we were yet sinners, Christ died for us (Romans 5:8, John 3:16-17).
In John 14:15, Jesus tells his apostles what it means to love Him -- "If you love Me, you will keep My commandments."
In sum, we obey Christ because we love Him, and we love Him because He first loved us.
If you are like me, and have done things that are not morally right, that do not glorify God, then the Bible teaches that you deserve death (Romans 6:23). However, if you put your faith in Jesus, then He has paid the fines with His own shed blood for all of your immoral behavior (Colossians 1:19-23).
If you have not put your trust in Jesus Christ, there is no better time than now. The Bible states that if you confess with your mouth that Jesus is Lord and believe in your heart that God raised Him from the dead, you will be saved (Romans 10:9). God will then transform you, and you will then know how to truly love (1 John 4).