St. Thomas Aquinas
“This sacrament confers grace spiritually together with the virtue of charity… as Gregory observes in a Homily for Pentecost, ‘God’s love is never idle; for, wherever it is it does great works.’ And consequently through this sacrament, as far as its power is concerned, not only is the habit of grace and of virtue bestowed, but it is furthermore aroused to act, according to 2 Cor. 5:14: ‘The charity of Christ presseth us.'”
Source: St. Thomas Aquinas, Summa Theologica