Hiding the thumb-When and why:

In Halacha, we find recorded in the following areas that the thumb is to be hidden:

1. During prayer: There are certain regulations and restrictions of hand positions during the prayer of Shemoneh Esrei, such as not to stand with one’s hands on one’s thighs.[1] As to the preferred method of hand positioning, there are different customs amongst different societies, based on how it is customary to stand before the king when speaking with him and making a request.[2] In general, however, it is best to stand with one’s right hand over one’s left hand.[3] Now, some are accustomed due to reasons that are known to them, to hide their thumb within their palm and not show it during prayer.[4] [The right thumb is hidden within the right palm, and the left thumb is hidden within the left palm.[5] This is based on the teachings of Kaballah, as recorded by the Rameh in name of the Ramak. The reason explained behind why the thumb should be covered is because thumbs come from Gevura, and during prayer one is meant to hide the severities within the aspects of kindness, and hence incorporate the severities within the kindness and sweeten them.[6] A source for this can be drawn also from Halacha, in which we find that in the Temple it was forbidden for thumbs to be shown during the lottery.[7]]
2. During Havdalah: During Havdalah, when we place our hands in front of the flame in order to look at them and benefit from its light, one to enclose his four fingers over his thumb thus hiding his thumb within his fist.[8] According to Halacha, this is done to simply make it easier to see one’s palm and four fingernails at the same time.[9] However, according to Kabbalah, this is done in order so one does not see his thumb [seemingly due to the same reason recorded above].[10]

_____________________________________________________

[1] Admur 95:4; Michaber 95:3; Rambam Tefila 5:4; Brachos 24b

[2] Admur 95:4; M”A 95:2; Mahariy Abuhav

[3] Admur 95:4; Michaber ibid; Rambam ibid

[4] Admur 95:4; M”A 95:2; Asara Mamaros Mamar Eim Kol Chaiy 1:33 in name of Ramak; Elya Raba 95:5; Beir Heiytiv 95:1 in name of Arizal; M”B 95:6; Kaf Hachaim 98:13

[5] Machatzis Hashekel ibid

[6] Asara Mamaros ibid “To incorporate Midas Hadin within Midas Harachamim”; Machatzis Hashekel on M”A ibid; Pirush Yad Yehuda on Asara Mamaors that the thumb is Midas Hadin; Mahariy Tzalach on Eitz Chaim p. 40b that the thub represents severities

[7] Asara Mamaros ibid

[8] Admur 298:6; Siddur Admur; Beis Yosef 298; Shibulei Haleket 130

[9] Admur ibid; M”A 298:5

[10] Siddur Admur; Shaar Hakavanos 15b; Kaf Hachaim 298:19; See Kuntrus Hashulchan 138