St. Thomas, Summa:
Question: Whether every lie is a sin:
I answer that: An action that is naturally evil in respect of its genus can by no means be good and lawful, since in order for an action to be good it must be right in every respect: because good results from a complete cause, while evil results from any single defect, as Dionysius asserts (Div. Nom. iv). Now a lie is evil in respect of its genus, since it is an action bearing on undue matter. For as words are naturally signs of intellectual acts, it is unnatural and undue for anyone to signify by words something that is not in his mind. Hence the Philosopher says (Ethic. iv, 7) that “lying is in itself evil and to be shunned, while truthfulness is good and worthy of praise.” Therefore every lie is a sin, as also Augustine declares (Contra Mend. i).
With respect: St Thomas Aquinas never had occasion to hide Jews from the Nazis.
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IV. RESPECT FOR THE TRUTH
2488** The
right to the communication** of the truth is not unconditional. Everyone must conform his life to the Gospel precept of fraternal love. This requires us in concrete situations to judge whether or not it is appropriate to reveal the truth to someone who asks for it.
2489 Charity and respect for the truth should dictate the response to every
request for information or communication. **The good and safety of others, respect for privacy, and the common good are sufficient reasons for being silent about what ought not be known or for making use of a discreet language. **The duty to avoid scandal often commands strict discretion. **No one is bound to reveal the truth to someone who does not have the right to know it.283 **
2491 Professional secrets - for example, those of political office holders, soldiers, physicians, and lawyers - or confidential information given under the seal of secrecy must be kept, save in exceptional cases where keeping the secret is bound to cause very grave harm to the one who confided it, to the one who received it or to a third party, and where the very grave harm can be avoided only by divulging the truth. Even if not confided under the seal of secrecy, private information prejudicial to another is not to be divulged without a grave and proportionate reason.
2484 The gravity of a lie is measured against the nature of the truth it deforms, the circumstances, the intentions of the one who lies, and the harm suffered by its victims. If a lie in itself only constitutes a venial sin, it becomes mortal when it does grave injury to the virtues of justice and charity. **
How, pray tell, is the

Gestapo harmed by not knowing that Anne Frank is hiding in the attic??? Should I turn her over to the slaughterers, in the service of “truth”?
Jesus Christ **is **the Way, the
Truth, & the Life. I had rather save one of His brethren, than to serve bloody Hitler…If I hang for that–so be it!!
The law of Jesus’ day forbade reaping on the Sabbath, & the disciples plucked grain & ate it. Who was right, pray tell? The Pharisees or Jesus??
The Catechism would appear to support Jesus, & condemn the self-righteous legalism of the Pharisees.
In any case, my own choice is made: “For I could wish that I were accursed from Christ for [His Jewish] brethren, [His] countrymen according to the flesh,who are Israelites, to whom pertain the adoption, the glory, the covenants, the giving of the law, the service of God, and the promises; of whom are the fathers, and from whom, according to the flesh, Christ came, Who is over all, the eternally blessed God.”-- Romans 9:3.
But hey! That’s me…(

with, it appears, St Paul the Apostle in my corner…).