When you sit in your house excludes one who is occupied with a mitzvah - Further below the reason for this is explained

And when you walk on the road excludes the bridegroom - Even though the bridegroom is also engaged in a Mitzvah, were it not for an extra verse we would not derive it from the first verse, since "one who is engaged in a Mitzvah" is not written in the verse explicitly. Rather, we only derive an exclusion from "in your house", and from it we exclude one who is engaged in doing a Mitzvah where there is preoccupation. But a bridegroom , whose distraction is merely a preoccupation of thought, for he is thinking about the consummation of the marriage, if not for the additional verse we would not exclude.

One who marries a virgin is exempt - For his thoughts are occupied due to the mitzvah

How is this implied - That one who is engaged in a mitzvah is excluded

Like the way - "During your sitting" and "during your going" are juxtaposed with "the way".

Are we not dealing with etc. - That is to say, from where do we know that the verse is dealing with an optional journey exclusively? After all, the verse simply says "[when you walk on the] way", and consequently a journey for a mitzvah is also implied by it. Nevertheless the Merciful One says he should recite [the Shema].

If it is because of preoccupation - of the mind that exempts him, one whose ship sunk also [should be exempt]

Why did Rabbi Abba say - That is, why did he say even though he is preoccupied with this distress he is obligated in all of the mitzvot except from Tefillin, for "glory" is said regarding them to Ezekiel [in the verse] "bind your glory upon yourself etc.", thus they require glory. And the mourner rolls in his sorrow in dirt; there is no glory there.

He is preoccupied with a mitzvah - And since we are merely deriving a [specific] exclusion, namely, that a bridegroom is excluded, it is sufficient to exclude [the bridegroom] due to a mitzvah-related preoccupation.