The Mishnah Berurah (sk2) notes that the Mechaber’s discussion here basically concerns Minchah or even Shacharit, where the individual was still saying birkat keriat Shema when the congregation started its Amida and the question is whether he will be able to start and finish his personal Amida in time for Kedushah.
We might understand the Mishnah Berurah to mean that the individual’s only real concern is whether he will be finished in time for Modim. As far as Kedushah is concerned, he can always just stop in the middle of his Amida and listen intently as the chazzan and congregation say it. After all, “shome’a k’oneh – someone who hears is considered as if he says.”
Now, we must ask: Why this great concern with Modim? How is it more important than the other berachot in the Amida? Tosafot (s.v. “ad sh’lo yagia…”) addresses this question and explains that “he must bow [at Modim] with the tzibbur in order that he not appear as a kofer (a denier) of the one to whom the tzibbur is bowing.” Tosafot note that if an individual would reach Modim in his own Amida at the same time that the chazzan reached his in chazarat hashatz, that would be sufficient. But the Gemara is not talking about such a case.
Tosafot note that the requirement to bow with the chazzan does not refer to the individual’s Modim D’Rabbanan recital, for we do not find this as a reason in the Gemara. Tosafot reinforce this point with a description of how Rabbenu Tam acted when the chazzan reached Modim while he was still praying Shemoneh Esreh. Rabbenu Tam would stop and bow together with the tzibbur without uttering a word. He would only do so, however, if he was in the middle of a berachah, not at the end because the Gemara (infra 34a) rules that it is prohibited for one to bow at the conclusion of every berachah.
Nevertheless, Tosafot note that Rabbenu Tam’s solution is only a b’di’avad option. L’chatchilah, one should not utilize it. Obviously, it is far better to join a congregation at the beginning of prayers, but in this case, the adage “better late than never” applies.
(To be continued)
Rabbi Yaakov Klass, rav of Congregation K’hal Bnei Matisyahu in Flatbush, Brooklyn, is Torah Editor of The Jewish Press. He can be contacted at email@example.com.