The great day of Shavu`oth, the memorial of the giving of the Torah to Israel at Har Sinai through Moshe Rabbenu. A time to celebrate the Torah which separates the people of Israel from all other nations.
The Torah proclaims that HaShem is One; that there is no other Creator besides Him. One of the biggest forbidden things in the Torah is serving, worshiping, or even thinking about doing such. In fact, even if one defecates on an idol as an insult, if that is the way its worshipers praise this false deity, that person is still guilty of a sin, albeit an accident.
Merely giving the impression of serving any other god, even when one is not actually doing so, is forbidden. This is because a Jew must be seen as serving only HaShem, being that he is chosen for special service to HaShem, and any indication of foreign service is forbidden to the extreme.
So clearly, Shavu`oth has nothing to do with anything contrary to HaShem and His Torah. However, the Messianics and in fact all strains of Christianity say that on this day, there was a supposed outpouring of the "Holy Spirit" on "Pentacost" which is their holiday partially derived from Shavu`oth.
The term in Hebrew is Ruahh HaQodesh (please note: "hh" refers to the guttural "h" sound of the letter "hheth"; whereas most people pronounce this the same as the letter "khaf", a "kh"/"ch" sound). I distinguish between this and the Christian concept of Holy Spirit. It is said that the followers of the Christian messiah had a day paralleled by the Shavu`oth account of the Torah being spoken by HaShem in all the 70 languages of the goyim. What is claimed to have happened is people "speaking in tongues".
Speaking in tongues is meant in the NT to mean speaking in foreign languages at random. Whereas today, the Pentacostal sect of Protestant Christianity as well as some Messianics and other Christians know it is unintelligible speech as well as foreign languages.
So what is the point of all this?
"Speaking in tongues" may be random jibberish, a form of demonic influence on speech, or be a mixed spiritual experience; or it could be all of those or any combination of those. The point is, people who worship a foreign entity and breach a basic law of Torah - to serve only HaShem - are not in a position for spirituality in qedusa, rather they partake in the side of qelipa; the other side.
In other words, the Pentecost and the "Holy Spirit" of the goyim and of `avoda zara are the sittra ahhra (other side) version of what is in true Torah-Judaism.
Just as I learned earlier today on Shabat (it is motza"sh as I am writing this), in Liquttei Moharan, torah 8, the sighing of a Jew is great. The breath (neshima) is related to the soul (neshama) and has to do with the ruahh (spirit/wind/breath) of life that HaShem breathes into creation. The sigh of the Jew, fills the hhesron (lack) which exists in a given thing because of a lack of 'ruahh' in that thing. This sigh draws life into the thing.
On the flip side, the resha`im (the evil) symbolized by `Esaw who is "ish se`ir" draw their fulfillment of lack from the other side in what is a "ruahh se`ara" (storm wind), which is strong temporarily but results ends up sweeping away the bodies and souls of those who use it.
This "Holy Spirit" of the Christians is an aspect of `Esaw, the "ruahh se`ara"/storm wind, which has strong but temporary strength, and eventually passes away like every storm, bringing the bodies and souls of those who are caught up in it away into destruction. As we see, Christianity is passing away; and Messianism will either result in the currently non-Jewish, potential Jewish souls eventually coming to true Torah or the withering away of their lives.