I read that St. Thomas Aquinas said:
To one who has faith, no explanation is necessary. To one without faith, no explanation is possible.
Where did St. Aquinas say this?
It appears to be a loose paraphrase of S.T. II-II, Q. 1, Art. 5, reply obj. 1: "Unbelievers are in ignorance of things that are of faith, for neither do they see or know them in themselves, nor do they know them to be credible. The faithful, on the other hand, know them, not as by demonstration, but by the light of faith which makes them see that they ought to believe them, as stated above" (A. 4, ad 2, 3).
The paraphrase is a potentially misleading oversimplification, though, as you can see from S.T. II-II, Q. 2, Art. 10, "Whether Reasons in Support of What We Believe Lessen the Merit of Faith." Basically, one who has faith doesn't care whether explanation is strictly
necessary, because "when a man's will is ready to believe, he loves the truth he believes, he thinks out and takes to heart whatever reasons he can find in support thereof; and in this way human reason does not exclude the merit of faith but is a sign of greater merit." And, although one without faith can't be sufficiently led to faith by explanation of doctrines, nevertheless the "reasons which are brought forward in support of the authority of faith [...] remove obstacles to faith, by showing that what faith proposes is not impossible." If it were not so, St. Thomas would not have written this:
It is written (1 Pet. 3:15): "Being ready always to satisfy every one that asketh you a reason of that faith [*Vulg.: 'Of that hope which is in you.' St. Thomas' reading is apparently taken from Bede.] and hope which is in you." Now the Apostle would not give this advice, if it would imply a diminution in the merit of faith. Therefore reason does not diminish the merit of faith [S.T. II-II, Q. 2, Art. 10, sed contra].
So the truth is that, to one who has faith, explanation is eminently desirable, to the extent that it's possible; and to one without faith, explanation is possible, to the extent that it can remove what falsely appear to be persuasive rational objections to faith. The paraphrase deviates so far from this truth as to be seriously misleading, and it doesn't accurately represent St. Thomas's thought on the relationship between faith and reason.
Blessings,
Don McMaster