We all have a vague idea that virtue is something good and that vice is something bad. And, in general terms, that’s true.
We could simply call virtue a good habit and vice a bad habit. A habit is something which we get by doing the same action over and over again. A habit makes it easy for us to carry out that particular action. So, if I make an effort to be on time every day at work, it will eventually become second-nature for me to be on time. Conversely, if I drink heavily every Friday evening, it will eventually become second-nature for me as well.
In religious terms, virtue is a habit of good works and vice is a habit of sin. But, in order to get to heaven and to love God as he deserves to be loved, I have to do good and avoid sin. Therefore, ultimately, virtue leads me to heaven, while vice leads me to hell. As a result, it is of the utmost importance to acquire virtues and to root out vices.
The good news is that, if we work on acquiring virtue, we will be automatically rooting out vice. This is because virtue and vice are opposites and are mutually exclusive.
To see how this works, let’s take the example of our attitude towards alcohol. Alcohol is a good thing in itself, but we can abuse it if we don’t take it in moderation. The virtue we need in order to control our use of alcohol is called Temperance (another word for moderation). What do I have to do to get the virtue of Temperance? I have to be moderate in my use of alcohol a certain number of times. Eventually, it will become easy for me to control my consumption of alcohol. If, on the other hand, I regularly drink too much alcohol, I will acquire the vice of Intemperance. It will be equally easy for me to drink too much when I have this vice.
But, experience tells us that it is much easier for us to acquire vices than virtues. This is because of the results of Original Sin which, even though it has been pardoned in Baptism, leaves our souls weak and inclined to sin. As a result, our efforts are never enough on their own to get rid of vice and acquire virtue. We need the Grace of God, which we can get through prayer and the Sacraments (particularly Confession and Holy Communion). God is all-powerful and with His strength we can do all things.