Berakhot 16B

אי הכי מאי איריא הכונס את הבתולה? אפילו כונס את האלמנה נמי.

The Talmud questions this: If so, why discuss a case of one who is marrying a virgin in particular? Even one who is marrying a widow is performing a mitzva and should also be exempt.

הכא ⁠— טריד, והכא ⁠— לא טריד.

The Talmud responds that nevertheless, there is a distinction between one marrying a virgin and one marrying a widow. Here, in the case of one who marries a virgin, the groom is preoccupied by his thoughts, while here, in the case of one who marries a widow, he is not preoccupied.

אי משום טרדא, אפילו טבעה ספינתו בים נמי, אלמה אמר רבי אבא בר זבדא אמר רב: אבל חייב בכל מצות האמורות בתורה, חוץ מן התפילין שהרי נאמר בהן ״פאר״, שנאמר ״פארך חבוש עליך וגו׳״!

The Talmud challenges: If a groom is exempt from the recitation of Shema simply due to preoccupation, then even one who is preoccupied because his ship sank at sea should be exempt. If so, why then did R' Abba bar Zavda say that Rav said: A mourner is obligated in all the mitzvot mentioned in the Torah except for the mitzva to don tefillin, as the term splendor is stated with regard to tefillin, as it is stated that the prophet Ezekiel was prohibited to mourn and was told: “Bind your splendor upon yourself” (Ezekiel 24:17). If even a mourner, who is pained and preoccupied, is obligated to recite Shema, clearly preoccupation has no bearing upon one’s obligation.

אמרי התם טרדא דרשות הכא טרדא דמצוה.

The Talmud responds: Nevertheless, there is a distinction between the cases. There, it is a case of preoccupation with a voluntary act, as there is no mitzva to be preoccupied with his mourning, but here, in the case of a groom, the cause of the preoccupation is the mitzva itself.