פירוש על סוכה 49:5

Gemara: In your sitting in your house exempt one involved in a mitzvah - ...that he is not obligated in reading the Shema and later it is explained what the implication is.

And in your going in the road exempts a groom - ...and even though he is also occupied in a mitzvah, a second verse is needed for him. For if the first had been written, since a groom was not explicitly written in the verse, I would have thought that the verse only exempts one who is burdening and doing the work of a mitzvah with his hands, or traveling for a mitzvah, but a groom, who sits idle and is not involved except for his preoccupation in contemplating marital relations, is not exempted by the verse. Therefore, the additional text teaches us that he is exempt from reading the Shema, for he is preoccupied in contemplating about marital relations.