I do not know how it is, that after the foolish remarks which he has made upon the subject which we have just been discussing, he should add the following, that “God does not desire to make himself known for his own sake, but because he wishes to bestow upon us the knowledge of himself for the sake of our salvation, in order that those who accept it may become virtuous and be saved, while those who do not accept may be shown to be wicked and be punished.” And yet, after making such a statement, he raises a new objection, saying: “After so long a period of time, then, did God now bethink himself of making men live righteous lives, but neglect to do so before?”
To which we answer, that there never was a time when God did not wish to make men live righteous lives; but He continually evinced His care for the improvement of the rational animal, by affording him occasions for the exercise of virtue. For in every generation the wisdom of God, passing into those souls which it ascertains to be holy, converts them into friends and prophets of God. And there may be found in the sacred book (the names of) those who in each generation were holy, and were recipients of the Divine Spirit, and who strove to convert their contemporaries so far as in their power.
Source: Against Celsus (New Advent)