You seem to have pretty good discussions in your religion class. You must be quite a group with quite the teacher.

Lets see if I can shed a little light on the subject.

First of all, about the commandments. The young man said he had fulfilled all the commandments, and it was true, he had fulfilled all the commandments he knew about. However, Christ came to give us a new commandment, to love one another as I have loved you, and you know how he showed his love, by forgetting about himself, laying aside all consideration of himself, coming to serve us and going so far as to die on the Cross to save us from our sins. You will notice that the Gospel says that when Jesus looked at this young man he loved him. He loved him so much He wanted to take him to a new level, to bring him closer to Himself, make him more like Himself, give him a share in His own mission of saving others. And so He made the invitation, If you want to be perfect, sell all you have, give it to the poor, and follow me. This is where the young mans riches got in the way. Not only had he many possessions, he was also attached to them, he was not ready to give them up when somebody else needed him. So you can see that it is much more difficult to really love to the point of giving your life, than to fulfill external commandments (honor your father and your mother, do not kill, etc). Love is the biggest challenge because in order to love you have to give yourself.

Then, what happened afterwards? The young man went away sad. He really wanted to be perfect but he didnt want to pay the price, and so he was divided. For perhaps the first time in his life his money could not buy him happiness. Jesus, I think, was also sad too to see him go away. Jesus wanted him to be happy, He wanted him to have what was best, but the man chose what was less, and went away sad.

Now, do you commit a mortal sin when you turn your back on God and reject a vocation? To commit a mortal sin there are three conditions: grave matter, full knowledge and full consent.

I think a vocation that is clearly seen may be grave matter, because there is so much good that can come from it that will be lost if we dont follow it. But I also think that we are not always aware of that; when we turn our backs on God we know not what we are doing. Seeing that the knowledge of a vocation is in a great measure an act of faith, it is hard to know just how much knowledge there really is (this is why prayer is so necessary if we are going to discover our vocation).

And there is also the question of our freedom. Sometimes the pressures of family opposition, the power of peer-pressure and human respect, the power of an otherwise good friendship with someone of the opposite sex, even sometimes the effects of a stupid imprudence (an accident from reckless driving that makes it impossible to follow the vocation), there are so many elements that can enter into play that I would not dare to say it is always, or sometimes a mortal sin not to follow the vocation. The most I would say is that in some cases it might be.

One thing I can say for sure, however, is that Gods reaction to our sin is not revenge but mercy. All you have to do is look at Christ on the Cross to know that.

And this gives us the answer to your final question. No matter what our sins are, no matter how grave they are, no matter how we damage Gods plan with them, God does not want us to die in our sin. He wants us to turn back to him. He wants to turn even our mistakes into good. If we are sincerely sorry for our faults and sins, if we turn back to Christ and seek his forgiveness (in the sacrament of Reconciliation, if they are mortal sins), he picks us up like that lost sheep and brings us back to the waters of life. If we love him we all feel a continued sadness for the times we failed him, even after he forgives us, but it is a sadness that makes us want not to let him down again. So yes, there is life after sin; Christ will always open up a path to the man who turns back to him, and we can always find our happiness in knowing that Christ looks forward and not backward once he has forgiven us.

I hope these thoughts help a little. God bless.