As per my comment above where I placed the link (see my comment above) I would like to translate, summarize and explain some ideas in order to make sense of this deep teaching of the Bal Shem Tov (sorry if its too long, I tried my best to shorten it as much as possible):
The word וַיִּקְרָ֖א has a small aleph, why? The Bal Haturim explains, “the א of ויקרא is written as a small letter because Moshe wanted to write ויקר (and it happened), the way it is written regarding Bilaam, which implies God appeared to him only as a chance occurrence. God, however, told him to write the א which indicates His love, but Moshe made it small.” However why in Shemot 19:20 does the Torah use a regular aleph? In Shaar Hakavanot Inyan Mizmor Shir Shel Yom Hashabba page 66 it says that on Matan Torah Moshe merited to get 1000 lights (crowns) that's why in Shemot 19:20 there is a regular aleph (to show this idea), but when Bnei Yisrael sinned Hashem told Bnei Yisrael in Parshat Vayikra 1:1 to write Vayikra with an aleph and the interpretation will be that Moshe still has one light/crown with him, but Moshe in his humbleness wanted to diminish the letter in a sense to say that it was his fault because he accepted the Erev Rav which in effect caused the Cheit Haegel.
In Rosh Hashana 21b it says, “The aforementioned verse states: “The words of the Lord are pure words…purified seven times [shivatayim].” Rav and Shmuel disagreed about a matter relating to this verse: One of them said: Fifty gates of understanding were created in the world, and all of them were given to Moses, except for one gate, for it is stated: “The words of the Lord are purified shivatayim,” which he understands to mean seven times seven, i.e., forty-nine, and it is stated: “And You have made him a little less than God” (Psalms 8:6). God created fifty gates of understanding, but He made man a little lower than God, giving him only forty-nine of them.”
Why does the Gemera say 50 minus one and not just 49? In Lekutei Torah in Vaetchanan the Arizal explains that at Matan Torah Moshe Rabbeinu received the 50 gates of understanding and when the Cheit Haegel happened he told him לך רד, go down, and he lost only the 50th level (and Gematria of לך רד equals 50, meaning go down from the 50th level). We are told in the Gemera in Avodah Zara 5a it says, “Rabbi Yosei says: The Jewish people accepted the Torah only in order that the Angel of Death would not rule over them, as it is stated: “I said: You are godlike beings, and all of you sons of the Most High” (Psalms 82:6), i.e., they had become immortal like angels. Then, God states: After you ruined your deeds, “yet you shall die like a man, and fall like one of the princes” (Psalms 82:7).” So when Moshe Rabbeinu received the 50 gates of understanding at Matan Torah, that 50th level was able to defeat the Malach Hamavet and cause no sickness or death to come to the world, however after Cheit Haegel when Moshe lost the 50th gate, sickness and death returned to the world.
From within the 1000 lights within the 50th gate Moshe was left with one light where he was able to bring down healing to Bnei Yisrael. Now that Moshe is not with us how do we get healing? We know based on various sources mentioned in the link that whoever learns Torah which Moshe Rabbeinu gave over to us gets the one light of healing within the 50th gate that was with Moshe, and that brings all the healings that Bal Shem Tov spoke about.
