II. God's plan was always partially understood, and is now of universal application
This plan of God's mercy and justice, though in the ages past it was in a measure enshrouded in darkness, was yet not so completely hidden that the saints, who have most merited praise from the beginning till the coming of the Lord, were precluded from understanding it: seeing that the salvation, which was to come through Christ, was promised both by the words of prophecy and by the significance of events, and this salvation not only they attained who foretold it, but all they also who believed their predictions.
For the one Faith justifies the saints of all ages, and to the self-same hope of the faithful pertains all that by Jesus Christ, the Mediator between God and man, we acknowledge done, or our fathers reverently accepted as to be done. And between Jew and Gentile there is no distinction, since, as the Apostle says, “Circumcision is nothing, and uncircumcision is nothing, but the keeping of God's commands,” and if they be kept in entirety of faith, they make Christians the true sons of Abraham, that is perfect, for the same Apostle says, “For whosoever of you were baptized in Christ Jesus, have put on Christ.
There is neither Jew nor Greek: there is neither slave nor free: there is neither male nor female. For you are all one in Christ. But if you are Christ's, then are you Abraham's seed, heirs according to promise.”
Source: Sermons (New Advent)