Wild Animals will become Tame

The wolf, shall dwell with the lamb; and the leopard, shall lie down with the kid..

An infant shall play on the cobra's hole, and a child shall reach into the viper's nest. They shall neither hurt nor destroy in all My holy mountain, for the earth shall be filled with the knowledge of G-d, as the waters submerge the sea." [5]

Accordingly, the Messianic ideal, is not a world, in which everything with a negative trait or potential disappears; but one in which these traits and potentials are eliminated, and the energies that sustain them, are redirected to positive and G-dly ends.
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On Passover, Chametz is utterly rejected: we are forbidden to eat it, derive benefit from it in any way, or even keep it in our possession; there is even a special mitzvah to destroy all leaven that is in our possession on the eve of the festival.

On Shavuot, however, not only is Chametz permitted, and the Torah even commands that two loaves of leavened bread be offered on the altar in the Beit Hamikdash (the Holy Temple in Jerusalem) --- something that is strictly forbidden not only on Passover but all year round.

Leaven, whose primary feature is that it rises and inflates itself, represents the source of all evil in the heart of man: arrogance and pride. But the sefirah-count is the process, through which we sublimate the forty-nine adverse derivatives of pride.

Until we reach the point, that it is divested of its negativity, and now can be included in the G-dliness of the Beit Hamikdash --- Which constituted a "taste" of a future world, that shall be "wholly Shabbat and tranquility, for everlasting life."
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Rabbi Shimon says, that only the destructive nature of "evil beasts" will be terminated, but they continue to exist, in their new peaceful and harmless state.

Rabbi Shimon says, hashbatah implies only the termination of a thing's particular characteristics --- in this case, the destructive nature of "evil beasts."

It is this aspect or feature of their being that G-d will eliminate, while they continue to exist in their new peaceful state.