Sifrei on Deuteronomy
ויספו השוטרים לדבר אל העם ואמרו, למדנו שהם הדברים [של עצמם].
(Devarim 20:8) "Then the officers shall speak further to the people": their (the officers') own words (and not those of the Cohein).
מי האיש הירא ורך הלבב. שיש עבירה בידו, בסתר ילך ושוב לביתו.
"Who is the man that fears and that is soft of heart?": that fears because of his transgressions, as per the words of R. Yossi Haglili: Come and see how the L-rd was solicitous of one's dignity, Scripture attributing (his returning) to all of these (aforementioned) things to salvage the dignity of one who returns because of faint-heartedness — so that they say of him: Perhaps he (is returning because) he built a house or planted a vineyard or betrothed a woman.
רבי עקיבא אומר, הירא ורך הלבב כמשמעו. רבי יוסי הגלילי אומר, (הירא) ורך הלבב, זה בן (ארבעים) [ששים] שנה.
R. Akiva said: "that fears and that is faint of heart" is to be taken literally — He cannot stand in the ranks of battle and behold the drawn sword. And all had to bring proof (of building a new house, etc.), except the fearer and the faint-hearted, his proof being "with him," i.e., he hears the clashing of the shields and takes fright; the whinnying of the horses, and shakes; the blaring of the trumpets, and panics. R. Yossi Haglili says: "that fears and that is soft of heart": one who is forty (or older). If it is already written "that fears," why need it be added "and that is soft of heart"? To teach that even the bravest of the brave and the strongest of the strong — if he is merciful (i.e., "soft-hearted"), he returns, as it is written "and not melt the heart of his brothers as his own heart."
ולא ימס את לבב אחיו כלבבו. מלמד שאם היה אחר מתירא מן העבירה שבידו, כולם חוזרים ובאים.
"and not melt the heart of his brothers as his own heart." R. Shimon says: If one hears the words of the Cohein and (they apply to him) and he does not return, in the end, all will return because of him.