A spiritual discipline is a spiritual practice that you do. It is training one’s spiritual faculties and moral character. Prayer, for example, is a discipline, it is something that you do.
A virtue is a disposition that results in behavior that is good, beneficial, and pleasing to God it is the quality of one’s character.
The Difference
Disciplines are something you do, virtues are something you are. Humility is a virtue, humbling yourself is a discipline.
Although they are different, they are related. Humbling yourself leads to one gaining the virtue of humility. Acts lead to dispositions. This is important.
Sowing and Reaping
As Ralph Waldo Emerson once said, “Sow a thought and you reap an action; sow an act and you reap a habit; sow a habit and you reap a character; sow a character and you reap a destiny.”