Regarding His human nature, Christ received His fullness, such that through Him it is derived to all. Jn. 1:14: 'Full of grace and truth'. And a little later: 'And of His fulness we all have received, and grace for grace'. And 3:34: 'For God doth not give the Spirit by measure'. And so baptism and the other sacraments do not have efficacy except by virtue of the humanity and the passion of Christ.
[St. Thomas Aquinas, Commentaries on St. Paul's Epistles to Timothy, Titus, and Philemon, Baer, ed. and tr., St. Augustine's Press (South Bend, IN: 2007) p. 189. This is part of his commentary on Titus 3:6.]