HKB
"Who is this king of glory?" and (Isa. 63:1): "Who is this that cometh from Edom?" Therefore men were not bound to believe explicitly in the mystery of Christ's Incarnation.
Obj. 2: Further, it is evident that John the Baptist was one of the teachers, and most nigh to Christ, Who said of him (Matt. 11:11) that "there hath not risen among them that are born of women, a greater than" he. Now John the Baptist does not appear to have known the mystery of Christ explicitly, since he asked Christ (Matt. 11:3): "Art Thou He that art to come, or look we for another?" Therefore even the teachers were not bound to explicit faith in Christ.
Obj. 3: Further, many gentiles obtained salvation through the ministry of the angels, as Dionysius states (Coel. Hier. ix). Now it would seem that the gentiles had neither explicit nor implicit faith in Christ, since they received no revelation. Therefore it seems that it was not necessary for the salvation of all to believe explicitly in the mystery of Christ.
On the contrary, Augustine says (De Corr. et Gratia vii; Ep. cxc): "Our faith is sound if we believe that no man, old or young is delivered from the contagion of death and the bonds of sin, except by the one Mediator of God and men, Jesus Christ."
I answer that, As stated above (A. 5; Q. 1, A. 8), the object of faith includes, properly and directly, that thing through which man obtains beatitude. Now the mystery of Christ's Incarnation and Passion is the way by which men obtain beatitude; for it is written (Acts 4:12): "There is no other name under heaven given to men, whereby we must be saved." Therefore belief of some kind in the mystery of Christ's Incarnation was necessary at all times and for all persons, but this belief differed according to differences of times and persons. The reason of this is that before the state of sin, man believed, explicitly in Christ's Incarnation, in so far as it was intended for the consummation of glory, but not as it was intended to deliver man from sin by the Passion and Resurrection, since man had no foreknowledge of his future sin. He does, however, seem to have had foreknowledge of the Incarnation of Christ, from the fact that he said (Gen. 2:24): "Wherefore a man shall leave father and mother, and shall cleave to his wife," of which the Apostle says (Eph. 5:32) that "this is a great sacrament . . . in Christ and the Church," and it is incredible that the first man was ignorant about this sacrament.
But after sin, man believed explicitly in Christ, not only as to the Incarnation, but also as to the Passion and Resurrection, whereby the human race is delivered from sin and death: for they would not, else, have foreshadowed Christ's Passion by certain sacrifices both before and after the Law, the meaning of which sacrifices was known by the learned explicitly, while the simple folk, under the veil of those sacrifices, believed them to be ordained by God in reference to Christ's coming, and thus their knowledge was covered with a veil, so to speak. And, as stated above (Q. 1, A. 7), the nearer they were to Christ, the more distinct was their knowledge of Christ's mysteries.
After grace had been revealed, both learned and simple folk are bound to explicit faith in the mysteries of Christ, chiefly as regards those which are observed throughout the Church, and publicly proclaimed, such as the articles which refer to the Incarnation, of which we have spoken above (Q. 1, A. 8). As to other minute points in reference to the articles of the Incarnation, men have been bound to believe them more or less explicitly according to each one's state and office.