It is not possible for any Jew to observe all 613 commandments even when the Temple was standing. A case in point is that many Mitzvot apply only to Kohanim.

The Sefer Hachinuch wrote that it is a Mitzva that the Kohein blesses the Jewish people every day of the year. On days when the Mussaf prayer is recited, there is an additional blessing. In Israel, the Kohein blesses........

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