12 However, it was not by means of visions alone which were seen, and words which were proclaimed, but also in actual works, that He was beheld by the prophets, in order that through them He might prefigure and show forth future events beforehand. For this reason did Hosea the prophet take “a wife of whoredoms,” prophesying by means of the action, “that in committing fornication the earth should fornicate from the Lord,” that is, the men who are upon the earth; and from men of this stamp it will be God's good pleasure to take out a Church which shall be sanctified by fellowship with His Son, just as that woman was sanctified by intercourse with the prophet.
And for this reason, Paul declares that the “unbelieving wife is sanctified by the believing husband.” Then again, the prophet names his children, “Not having obtained mercy,” and “Not a people,” in order that, as says the apostle, “what was not a people may become a people; and she who did not obtain mercy may obtain mercy. And it shall come to pass, that in the place where it was said, This is not a people, there shall they be called the children of the living God.” That which had been done typically through his actions by the prophet, the apostle proves to have been done truly by Christ in the Church.
Thus, too, did Moses also take to wife an Ethiopian woman, whom he thus made an Israelitish one, showing by anticipation that the wild olive tree is grafted into the cultivated olive, and made to partake of its fatness. For as He who was born Christ according to the flesh, had indeed to be sought after by the people in order to be slain, but was to be set free in Egypt, that is, among the Gentiles, to sanctify those who were there in a state of infancy, from whom also He perfected His Church in that place (for Egypt was Gentile from the beginning, as was Ethiopia also); for this reason, by means of the marriage of Moses, was shown forth the marriage of the Word; and by means of the Ethiopian bride, the Church taken from among the Gentiles was made manifest; and those who do detract from, accuse, and deride it, shall not be pure.
For they shall be full of leprosy, and expelled from the camp of the righteous. Thus also did Rahab the harlot, while condemning herself, inasmuch as she was a Gentile, guilty of all sins, nevertheless receive the three spies, who were spying out all the land, and hid them at her home; [which three were] doubtless [a type of] the Father and the Son, together with the Holy Spirit. And when the entire city in which she lived fell to ruins at the sounding of the seven trumpets, Rahab the harlot was preserved, when all was over [in ultimis], together with all her house, through faith of the scarlet sign; as the Lord also declared to those who did not receive His advent,— the Pharisees, no doubt, nullify the sign of the scarlet thread, which meant the passover, and the redemption and exodus of the people from Egypt—when He said, “The publicans and the harlots go into the kingdom of heaven before you.”
Source: Adversus haereses (New Advent)