Our Sages place great emphasis on executing a mitzvah from start to finish, rather than leaving it incomplete.
Nevertheless, when it is unclear what exactly constitutes completion of a particular mitzvah, we must examine the mitzvah in question before rushing to complete it to the fullest measure. If the mitzvah is charity‑related or the like, we should obviously extend our involvement beyond any risk of leaving it incomplete. In other instances, however, we are best off fulfilling only the bare minimum, even at risk of not seeing the project through from beginning to end.
For example, when a beis din must inflict malkos, lashes, upon transgressors of certain sins, the Torah warns, “He shall flog him with forty lashes; he shall not exceed, lest he give him a more severe flogging than these.”
Since the Torah prohibits exacting excessive punishment, if we are in doubt regarding the extent of our obligations in this mitzvah, we suffice by fulfilling our duty to the bare minimum.
This explains the Midrash which discusses how the plague of frogs was set into motion. Aharon was instructed to afflict the Egyptians with frogs—plural—that would swarm through the entire land, yet the verse states, “Aharon stretched forth his hand... and the frog came up and covered the land,” implying that only one frog emerged through Aharon’s efforts. The Midrash explains that Aharon brought one frog from the Nile, but when people hit that frog, swarms of frogs miraculously streamed from it and covered the land.
Since G‑d’s instruction to Aharon involved inflicting pain on other human beings, the Midrash opines that Aharon was as minimally involved as possible in its completion; he drew only one frog out from the Nile, and allowed the rest of the plague to come about at the hands of others.
—Likkutei Sichos, vol. 16, pp. 84–85
