Q:

Catholic doctrine on spiritual vocation

I was reading Angelic Doctor about religious vocation (= a invation from God to life as dioceasn priest or in some kind of religous order (like Dominicans, Franciscans...)) and it seems that he did not view the matter as most view today. Among the things Aquinas says (in On The Perfection of the Spiritual Life - it is on end of chapter 8) is:

This solution of Augustine is in harmony with what was said above about poverty. For Abraham had so great spiritual perfection in virtue, that his spirit did not fall short of perfect love for God on account either of temporal possessions or of married life. But if another man who does not have the same spiritual virtues, strives to attain perfection, while retaining riches and entering into marriage, his error in presuming to treat Our Lord’s words as of small account will soon be demonstrated.

It would seem that according to Aquinas, one must, under the pain of sin of persumption, and if the one is able to (without any obvious impediments), pursue spiritual life of poverty and celibate. I am not sure that this is what Aquinas really wants to say, however, let me try to formalize possible argument (be it one from Aquinas or not) for a such position.
Let me organize the argument in six points (which I will justify in the edit if somone objects to some point in the comments). It goes something like this.

If one does not want to attain perfection, he sins mortaly.
Thefore if one wants to be saved, he must desire perfection.
Easier (more safe) path to perfection is via life of celibate and poverty.
Salvation is not easy to attain, therfore one must be at most careful to do anything that he can to attain it (or he commits a sin of persumption).
If one can chooses between more safe and less safe way to perfection he must take a more safe path, because if he choose less safe way he would not be at most careful to do anything to attain salvation.
Since more safe way is way of celibacy and poverty, and one must choose more safe way under pain of sin of persumption, it follows that one, if he is able to, must choose life of poverty and celibacy or else he sins.

If my argument does not work, I think that I may be failing to make some distinction, upon which one could desire the perfection and yet choose the less safe way without any sin. But how can one really desire perfection, if, when the better way is presented, he chooses the less safe way? Obviously if the better way is not presented one is excused. But what would be some examples that excuse somone that is not already married or suffers some serious impediment (like missing a hand,...)? Would that be having a passion and being good in some job (like a teacher or something) and long relationship with boyfreind or girlfreind? I take these two examples, because it seems to me, that youth today are most commonly thinking between those two and life of priest or life in some religous order. Would those two be reasnoble justfication for not following a better way, or are they obliged to leave everything for life as a priest or a life in some religous order? Do they sin if they do not leave everything (is it venial or mortal if it is even a sin)?
I am confused because this does not seem as common opinion of the Church, so any help would be great. Thanks.

A:

It seems you're asking about the difference between precepts and counsels. All are bound to follow the precepts (10 Commandments, Precepts of the Church, etc.), but a person not bound by religious vows does not sin by not living up to the counsels (poverty, chastity, obedience) to their fullest.
See:

St. Thomas Aquinas's question "Whether, in this life, perfection consists in the observance of the commandments [precepts] or of the counsels?" (Summa Theologica II-II q. 184 a. 3).
Fr. Antonio Royo Marín, O.P.'s Theology of Christian Perfection

p. 141 on the obligation of the laity to strive toward perfection,

We are all (religious and non-religious) obliged to strive for perfection (Mt. 5:48: "Be you therefore perfect").

p. 142 on choosing the better good.

cf. St. Thomas's commentary on Mt. 19:12 ("He that can take, let him take it [celibacy]."):Is not a man obliged to do the greater good? I say that one must distinguish the greater good in regard to the actual performance or in regard to the desire. One is not held to the greater good in regard to their actual performance, but to the desire to do them, because every rule and every action is determined to something defined and certain: but if one is bound to do every action that is better, one is bound to something uncertain. Hence, in regard to exterior actions, because one is not bound to do something uncertain, one is not bound to do the greater good; but in regard to the desire, one is held to desire the greater good. Hence, he who does not always wish to be better, cannot wish without contempt [of doing the greater good].** "There is a way of fulfilling this precept, so as to avoid sin, namely, if one do what one can as required by the conditions of one’s state of life: provided there be no contempt of doing better things, which contempt sets the mind against spiritual progress" (II II, q. 186, a. 2 ad 2um).Thus, married Christians must have the spirit of the counsels, even if they do not have the opportunity to put them into practice.

