Mishnah Berachos 3:2
“After they buried the deceased and returned, if they have sufficient time to begin to recite Shema and conclude before they arrive at the row, formed by those who attended the burial, through which the bereaved family will pass in order to receive consolation, they should begin [even if they will only have an opportunity to recite the first verse (Deuteronomy 6:4)].” – sefaria.org
From this we learn in the commentary, that the main part of the Shema prayer is the first verse; and, that this verse is minimally permissible to recite by a comforter, between the time after the deceased is buried, until reaching the line, where one would line up to approach and comfort the mourners, by offering one’s condolences. Seemingly so, the only motivating factor, according to halacha, to say the Shema at this time if necessary, would be if one was not able to do so that morning prior to the funeral. Incidentally, the Shema is a comforting prayer, in and of itself, and, if said, quietly to oneself, can offer divine consolation, regardless of who may take the opportunity to recite the prayer. Yet, it is forbidden to say the Shema while walking; so, this more or less throws a monkeywrench, figuratively speaking, of course, into the entire discussion.
Perforce, to say that these and similar guidelines within perek (chapter) 3:2, have to do with being exempt from performing a mitzvah, while engaged at the time with the performance of another mitzvah; for example, consoling a mourner. That so much consideration is given, in regard to the exact details of the situation, compels me to have more respect and appreciation of such a mitzvah. The gravity of the situation at a funeral, would certainly elicit proper respect towards the mourner and the mitzvah of consolation itself; yet, knowing that consoling a mourner takes precedence over the most important prayer in Judaism, demonstrates the kindness and compassion that we are to show to mourners. Also, this priority demonstrates as well, the kavanah (proper focus and intention) necessary to offer a meaningful consolation, without the distraction of having another mitzvah preoccupying one’s thoughts.
As an afterthought, I would add that Jewish mysticism teaches that every person has a divine spark within their soul, that originates with G-d. By treating others with respect, we are also honoring others as being created in G-d’s image. Therefore, I would imagine that G-d would not feel the least bit slighted in any way, if we set aside the obligation to say the Shema, for the sake of consoling a mourner.
Mishnah Berachos 3:3 has to do with more general exemptions and obligations, in regard to the following: tefillin (phylacteries), Shemonah Esrei, mezuzah, and Birchas HaMazon (Grace after Meals). Amongst the discussion on mezuzot is a commentary that obligates a father to make sure that a mezuzah is placed upon the doorpost of a child that lives alone. This is emotionally moving to me; and, I imagine the father himself placing the mezuzah on the doorpost of his child’s place of residence. For myself, this speaks of the continuity of values and traditions, within the framework of Judaism.