There is some news for you in the Old Testament that you just have to hear. Pick it up if you like, it's in Job chapter 7, verse 1. He speaks of battle and struggle. 

Doesn't that clear up a lot of things? 

fighting 

Here are a few more that will help us with our reflections. By all means look them up later because there are other interesting things said near where these come from, and you should always nourish your soul on God's word.  

St. Paul was a man who was familiar with fighting. But he always fought for a cause, he never wanted the type of shadow boxing we sometimes go in for. He was focused, like an athlete who trains to win the race. Listen to what he says: "I do not run aimlessly, I do not box as one beating the air, but I pummel my body and subdue it, lest after preaching to others I myself should be disqualified." (1 Corinthians 9:26-27) So he had a goal, and he was totally committed to that goal, and that commitment meant that he had to overcome some very serious opposition. And in the first line of that opposition he speaks about - his own body! His body didn't want to pay the price of serving God, he had to force it. You're probably thinking that this sounds kind of medieval. You're not the only one. I'm not going to contradict you, but if you say it is medieval you are taking the credit from St. Paul since he lived ages before that. And also St. John seemed to agree with him: "Do not love the world or the things in the world. If any one loves the world, love for the Father is not in him. For all that is in the world, the lust of the flesh and the lust of the eyes and the pride of life, is not of the Father but is of the world." (1 John 2:15-16) 

But the plot thickens. 

Christ himself might actually have agreed with them, or...maybe they even got it from him! "For whoever wishes to save his life will lose it...." (Matthew 16:25) 

So what St. Paul says is not just a "problem" that he had. He is pointing at something deeper and common to all followers of Christ. He does not seem to be talking about flagellation, but instead, about making the body follow orders and not give them. Our trouble is we take orders from our bodies, our bodily instincts, our spiritual instincts of pride, and we do not know how to go against them as saying yes to Christ would demand of us.  

growth  

St. Paul did not shirk this battle. And like all those who engage in it, he rose in the process to an enormous spiritual and human stature. He was no wild-eyed, thrashing, destructive zealot. He preached love constantly as the greatest of virtues, and then outdid his preaching with his actions. To bring the Good News to the gentiles he endured forty lashes minus one, he was beaten with rods...stoned...shipwrecked, he braved dangers from rivers, dangers from robbers, dangers from his own race, dangers from Gentiles, dangers in the city, dangers in the wilderness...in toil and hardship, through many sleepless nights, through hunger and thirst, through frequent fastings, through cold and exposure (2 Corinthians 11:24-27) and was the happiest of men in the process, the surest of men because he knew that once he had placed himself in subjection to Christ through God's grace then nothing or nobody could rob him of his love and his hope - who shall separate us from the love of Christ...? (Romans 8:35) 

It is fabulously engaging to think over and over about such a man. The authenticity; the energy; the choleric, driving commitment; and then to see how he steered and controlled and mastered his explosive temperament, and pushed his body to such limits, because he loved Christ tenderly, and his Church, and each individual member. At times he might have had to upbraid his Churches, but the most that got was attention; he is at his most compelling when he appeals to the love that Christ has shown them and that they must return in kind.  

You might be trying to slow me down by now, to tell me that I misunderstood your objection...that you know we will always have to fight, but the nature of your fight is different than St. Paul's, you are not fighting against sin which is outside you but sin which is inside you...in other words that you still fall into sin, and "big stuff" at that. That is why you are pretty sure that the vocation is not for you, even though at times the thought does come to you.  

Well, there is a relation between the two situations, but I think your first step is going to have to be to take stock of where you are. 

conscience 

Here are some guidelines/questions you should sit down and answer. Give them thought. Give them time. Come back to them a few times. Maybe even use a notebook as you work through them. 

First, a general question that is very fundamental: about your conscience. Does your conscience work right? In other words, is it well adjusted? Can you depend on it to give you an accurate reading of your standing before God?  

Two different types of things can go wrong with your conscience: one, it can be scrupulous, like a fuzzbuster that registers everything and goes off seven times a block, everything is an alarm: every mistake is exaggerated, every fault becomes impending condemnation (extreme case, but you see what I mean); or, second, it can be lax, not registering any danger, like the fuzzbuster that whimpers and gives you a timid blink when the trooper is already leaning in the window explaining the ticket. You are not in this last extreme because your question means that sin registers. But where do you stand on the scale in between? Is it just the big, big ones that get a reaction from you or do minor ones register too? 

There is a second general question that also has to do with your conscience. Your conscience needs input. It needs information, something to go by. Very often if things don't register in our conscience it is because we don't know that they should. Do you have what is called an informed conscience? Or are all your moral judgments just guesses? You can't get a good score on your SAT's by just guessing all the time, but sometimes we think we can lead perfectly good lives by guessing when it comes to right or wrong, or worse still, by following our feelings. Because we all know that if we ever did assignments on the basis of how we feel about them, it would take forever to graduate. So ask yourself, do I know the difference between what is right and what is wrong? 

Now, there is a prejudice here you will have to overcome. Let's call it the "gray hang-up." We all suffer from it to a greater or lesser degree, and it has nothing to do with senior citizens.  

Pressures around us have made us very sensitive people. We don't want to be perceived as simplistic or immature, or extremist, or judgmental, and the last thing we want to be accused of is seeing the world in "black and white." That is both naive and gauche today. You have to be "nuanced" and non-accusing. Because if you see some things are right and others are wrong, you imply that anyone who knowingly chooses what you see is right is a good person - and the one who knowingly chooses what you see is wrong is a bad person. And you shouldn't say things like that. Not in good company anyway. 

So you have to be gray if you are not going to be pointed at. And the grayer you are (neither white nor black, but quite the opposite) the smugger you can be. If you are quite gray and unidentifiable, you might even get to be allowed to point a finger or two at the sin of not being gray.  

examine 

Once you have made sure your conscience is working well and is informed you should look at what it is telling you. 

First, take a good look at your own standards and character. In the area of human virtue, have you set high enough standards for yourself (in your duties, studies, work...) and is your will strong enough to go for them consistently? How is your honesty and integrity? Do you have high intellectual standards? Are you content with mediocrity in your studies, in your recreational reading, in your grasp of the world and events? Do you have high moral standards? Do you just do what "everyone else" is doing?  

Questions like these will give you a sense of where you stand. 

Then, against the background of this information you can check your actual faults, starting with the general categories: 

Is your struggle with habitual mortal sin? And is it particularly in one area or in a few? 

Or have you gone beyond that and are now struggling with habitual venial sin? Is this narrowed to one area or are there several? 

Once you get the general feeling of how things are between yourself and God, get a good guide for examination of conscience that will take you through the commandments and virtues and help you get a precise picture of your situation. You will find that a good guide will enlighten you and help you continue to form your conscience. 

admit  

Or, if you prefer, own up. Generally it is called confession. It is pointless just to examine your life if it is not a step towards improving it. And the first improvement is to have God wash it clean. In our struggle against sin and in the continual improvement of our Christian life, the sacrament of reconciliation should never be conspicuous by its absence. Just like an athlete uses videos of his performance and their analysis by somebody more experienced to improve his output, so examination of conscience, confession, and spiritual direction should be considered the ideal way to progress in our spiritual life. 

resolution, improvement 

Examination and confession should never be brief interludes in an otherwise stagnant and unchanging life. They should be stepping stones and stages of development. Usually a good examination of conscience as well as telling you your faults will bring to light the circumstances that lead you to them: the occasions, people, places and things that are the prelude to your faulting, and at times your excuse for doing so. It can also bring us to see the good that we should be doing but aren't. Well understood, this realization is of the greatest help if you really want to progress. It shows you things you should avoid, and also hints at things you should start doing, if you are going to change for the better. But we need to make up our minds on these - and being human it helps greatly to have a regular confessor who can help us remain accountable for the good inspirations and resolutions God places in our heart.  

hope 

One of the most necessary virtues and attitudes to cultivate in our daily struggle is hope. It is also one of the most neglected. With God's help we can change. Hope gives joy and optimism and substance to our work. Hope is the key to resilience and perseverance. 

as regards vocation 

After all the above we can now come to some conclusions as regards the possibility of you, a sinner, being nevertheless called to serve God totally.  

The fact of having to struggle with sin in and of itself does not mean as much as the nature of this struggle, and the level it takes place at. And this is where you need a prudent confessor or spiritual director to help you.  

Some sins, because of their nature, can make it imprudent to attempt to follow a particular vocation. With others we might require special effort and help, but they still can be overcome. And then, to be under the influence of venial sin is not the same as to be having habitual trouble with mortal sin. 

One important point to note is that if you do not recognize you are a sinner, you will never understand the need for God's grace, and that would only make you get in its way in your attempt to be an apostle. 

Remember Peter in his boat after the miraculous catch? Lord, depart from me, for I am a sinful man. Christ, however, answered Fear not, from now on you will be a fisher of men.  

Take heart.