No, it is not a sin because God does not obligate us to follow a vocation in a way that would make it a sin to leave it, depending on the person. There are individuals who leave the seminary and may have done well to do so because they did not truly have a vocation. However, if this question refers to someone who genuinely had a divine vocation and left it, this is not a mortal sin at all. Mortal sin pertains to the violation of God's commandments, and this situation does not fall under that.
If someone truly had a vocation and, through error or weakness, abandoned it and chose another path, such as marriage and family, they can still sanctify themselves in their new vocation. Even though this new path may not have been the original plan of God, God is merciful and accepts their choice, granting blessings in that new vocation. It is a mystery, and while perhaps in eternity or purgatory, the person may recognize that they were meant to follow the original vocation, God's mercy allows them to find grace in the second path they chose. Ultimately, every vocation is a mystery between the soul and God, and only God knows the true culpability.
Dear visitors of Gloria Dei and all who have already written or who will write a personal message to me. I am grateful for your attention, your kindness, for your spiritual support and especially for your sacrifices and prayers for me. God may reward you!
