Is not following a vocation a sin? If someone does not follow his vocation, is it more or less impossible for him to live a holy life? Sometime ago I received such questions by e-mail, and now post them here (in edited form), with responses, with the hope that they will be helpful to others.
Are the harsh conclusions [drawn by St. Alphonsus de Liguori and Hans Urs Von Balthasar] that we risk even our salvation if we do not respond to a vocation (which seems to imply that it is a sin to say no to a vocation) is really a consequence of taking the personal approach to vocation? Don't these conclusions rather overlook a distinction that should be made within the personal approach? Don't they somehow present a unilateral idea of God's will or God's call? Even with God, there is a difference between His commanding something and offering something, between an invitation and a law. This is a rudimentary distinction and obviously these authors knew this: perhaps rejecting even an invitation from God, whose knowledge and will are perfect, must somehow come from a preference for something other than His will. But then what is the difference between a commandment and an invitation? There is clearly a difference in kind? One must be done and the other may be done. What does "may" really mean if rejecting it is saying no to God's will or loving something else in place of God's will? How can anything that comes from God really be an invitation?
Those conclusions don't really follow from the "personal approach" to vocation, but follow from misunderstandings that are often associated with the personal approach. But indeed, the mistake is not as simple as overlooking the distinction between a command and a invitation. (St. Ignatius is the only one I've seen who suggests that the words, "he who can take it, let him take it," may be a precept, rather than an invitation. This is possibly just an inexactness of language–something he said on the basis of a kind of intuition regarding the matter, but because he was not a learned theologian, articulated without the most precise terms.)
The severe conclusions seem to follow from a twofold narrow view of God: first, thinking of God as though his plan's for man were made independently of men's choices, and so are "ruined" by them; secondly, thinking of God as a human lover, who is really moved by disappointment or anger, and acts on this basis.
Both Alphonsus and Von Balthasar suggest strongly that it is often a mortal sin to knowingly reject a vocation. But even supposing this to be true, it would not follow that such a rejection would have the severe consequences they speak of–God could forgive this sin just as he forgives other sins, if one repents. Actually, for Alphonsus it seems to be rather the other way around: it is not so perilous because it is a sin, but it is a sin because it is so perilous for our salvation.
The difference between a commandment and an invitation is that a commandment is something imposed as necessary in order to be in loving union with the one commanding, an invitation is something presented as a way to be better united with the one inviting, but not necessary for such union. And therefore disobeying the commandment implies that one values something else more than one values union with God, and is a mortal sin, while rejecting the invitation implies only that one values something other than God without entirely referring its value to God. In itself, this is only a venial sin, or even only an imperfection.
The positions of Alphonsus de Liguori and Von Balthasar are presented in the book Paths of Love: The Discernment of Vocation According to Aquinas, Ignatius, and Pope John Paul II. You can also read more texts of Alphonsus on vocation and Von Balthasar on Vocation.
See also the post on Commandments and Counsels.