The Imam Ibn Rajab says, "For this tawhid (the oneness of Allah) is the greatest elixir." What does he mean by saying it is the elixir?

The questioner:
He says: Honorable Shaykh, may Allah grant you success. The Imam Ibn Rajab (may Allah have mercy on him) says, "For this tawhid (the oneness of Allah) is the greatest elixir. If a grain of it were placed upon mountains of sins and transgressions, it would turn them into good deeds." What does he mean by saying it is the elixir?

The Shaykh:
The elixir is the original meaning; the elixir is the essence. Yes.

The questioner:
He says: Honorable Shaykh.

The Shaykh:
The one who practices tawhid (the oneness of Allah) may have all his sins forgiven by Allah. In the Qudsi Hadith, Allah says: "If you came to Me with earth-full of sins, then came to Me I would come to you with earth-full of forgiveness." Tawhid (the oneness of Allah) expiates sins.
Allah may expiate all sins by it, or He may punish the sinners according to their sins and then bring them out to Paradise because of their tawhid (the oneness of Allah). The one who practices tawhid (the oneness of Allah) must enter Paradise. The one who dies upon tawhid (the oneness of Allah) must enter Paradise, either immediately or after being punished in the Fire according to his sins. Only the people of shirk (associating partners with Allah) and kufr (disbelief) abide in the Fire eternally, may Allah protect us from that. Yes.