19 The case standing thus, suppose, as I said, that we are now for the first time seeking unto what religion we shall deliver up our souls, for it to cleanse and renew them; without doubt we must begin with the Catholic Church. For by this time there are more Christians, than if the Jews and idolaters be added together. But of these same Christians, whereas there are several heresies, and all wish to appear Catholics, and call all others besides themselves heretics, there is one Church, as all allow: if you consider the whole world, more full filled in number; but, as they who know affirm, more pure also in truth than all the rest.
But the question of truth is another; but, what is enough for such as are in search, there is one Catholic, to which different heresies give different names whereas they themselves are called each by names of their own, which they dare not deny. From which may be understood, by judgment of umpires who are hindered by no favor, to which is to be assigned the name Catholic, which all covet. But, that no one may suppose that it is to be made matter of over garrulous or unnecessary discussion, this is at any rate one, in which human laws themselves also are in a certain way Christian.
I do not wish any prejudgment to be formed from this fact, but I account it a most favorable commencement for enquiry. For we are not to fear lest the true worship of God; resting on no strength of its own, seem to need to be supported by them whom it ought to support: but, at any rate, it is perfect happiness, if the truth may be there found, where it is most safe both to search for it and to hold it: in case it cannot, then at length, at whatever risk, we must go and search some other where.
Source: On the Profit of Believing (New Advent)