One of the laws regarding Grace After Meals is that of rinsing the hands before reciting the blessings, known as "mayim acharonim", literally "after-waters".
Know that the "Other Side" hovers over the table, as is described in the Zohar (Zohar II:154a,b) and can gain control over an individual more than it can at other times.
As described in the Zohar, eating and drinking by their nature bolster a person's material orientation, thereby desensitizing him to spirituality and divinity. One is thus, after having eaten his full, particularly susceptible to the power of evil.
This is particularly true if he has eaten by himself, and there are not three to recite Grace together. For the Invitation to Recite Grace drives away Other Side from there, as is mentioned in the Zohar (Zohar III:186b) regarding the incident of the young child.
According to Jewish law, if three or more men or three or more women have eaten bread together, they must recite Grace together. One of the party acts as the leader and formally invites the others to join him in reciting Grace. The positive energy generated by their camaraderie overcomes the negative power of evil…
In the Zohar, it is recounted that the young, orphaned son of Rabbi Hamnuna the Elder possessed great spiritual perception and mystical knowledge of the Torah. One of the teachings he shared with his guests, two students of Rebbe Shimon bar Yochai, was that when the Invitation to Recite Grace is recited, it weakens the power of evil present at the table.
The collective power of the three individuals' divine souls and the positive energy generated by their camaraderie overcomes the negative power of evil. This occurs, however, only when they consciously combine their individual energies together to recite Grace, that is, to focus on the spiritual dimension of the meal rather than simply the sensual pleasure of eating. Hence the power and importance of the Invitation to Recite Grace.
A person must therefore be very careful to have the proper intentions when rinsing his fingertips after the meal, in order that [the Other Side] not prosecute him.
Whenever a person succumbs to the temptations of evil, the sin he performs acts as a "prosecutor" against him in the heavenly court.
For by giving it this gift, as is known, the Other Side departs, leaving [the person alone]. In the beginning [of the meal] it is just a guest, but if the individual does not recite Grace with the proper intention and concentration it becomes the host and prosecutes against him. As we said, this is particularly true if one dines by himself, without the [protection offered by the] Invitation to Recite Grace.
Rinsing the remains of the meal off the fingertips is seen as "throwing the dog a bone." Evil possesses no intrinsic power; it derives its power solely by virtue of man's misdeeds. However, it must be present to at least some minimal extent in order for there to be free choice. If evil receives this minimal sustenance, it is satisfied, and, realizing that it has nothing more to expect from this meal, departs.
The mystical meaning of this statement is thus that when washing the fingertips after the meal one must meditate on the name Eh-yeh.
Now, one should not make any interruption between rinsing the fingertips and reciting Grace After Meals. I [Chaim Vital] was once with my master [the Ari] and someone came to me and said that he had been suffering from severe shoulder pains for two days. My master looked at him and said that this pain came from his having interrupted between rinsing the fingertips and reciting Grace After Meals by studying a chapter of the Mishna. He thus transgressed the instruction of our sages to proceed directly from the rinsing to the blessing. (Berachot 42a) In so doing, he transmuted the word for "directly" [in Hebrew, "teikef", spelled tav-kaf-pei] into the word for "shoulder" ["kateif", kaf-tav-pei] and he felt the pain there. One must not make any interruption between the rinsing and the recital of Grace…
From this we see that one must not make any interruption between the rinsing and the recital of Grace, even with words from the Torah. If one wishes to converse [at his table] in the Torah, as our sages have said one should, he should do so before the rinsing of the fingertips.
By not allowing any interruption between rinsing the fingertips and the recitation of Grace, the individual demonstrates that they form one conceptual unit, that is, the spiritual meaning of the former is also that of the latter.
Nonetheless, one should recite the following verses after rinsing the fingertips, before beginning the Grace After Meals: the entire Psalm 67, and then the verse, "I will bless G‑d at all times; His praise is always in my mouth." (Psalms 34:2) This is because the Other Side hovers over the table, as we have said, and it is called "at all times", as in the verse, "He must not come into the sanctuary at all times." (Lev. 15:2) The person…is declaring his wish to orient his consciousness toward the divine dimension of eating…
The Torah commands that the High Priest not enter the Holy of Holies whenever he wants ("at all times"), but rather only on the day of Yom Kippur. In this context, the phrase "at all times" is seen as something that prevents one from entering the realm of holiness, i.e., evil. Reciting the verse "I will bless G‑d at all times" is thus seen as a formula that neutralizes the power of evil present at the table.
It is interesting to note that Yom Kippur, the one day when the Torah allows the High Priest to enter the inner sanctum of the Temple, is a total fast day. On this day, of course, the evil that can potentially become empowered through the process of eating is not operative.
In order to remove [the evil] from there [i.e. the table], one must recite [the Invitation to Recite Grace, i.e.] "Bring us [the goblet] and we will bless", as is stated in the story of the young child in the Zohar. We therefore recite the verse "I will bless G‑d at all times…", in case a person is eating by himself and cannot say "Bring us and we will bless".
One should then say: "Ultimately, all is known: fear G‑d and observe His commandments, for this is the whole purpose of man." (Ecclesiastes 12:13)
Then, one should say: "My mouth will utter the praise of G‑d, and let all flesh praise His holy Name forever", (Psalms 145:21) "And we will bless G‑d from now to all eternity. Praise G‑d", (Ibid. 115:18) and "And he said to me, this is the table that is before G‑d". (Ezekiel 41:22)
[Note: In Rabbi Shneur Zalman’s formulation of the liturgy, all the above save this verse is recited before rinsing the fingertips.]
Only then should he commence Grace After Meals.
The common denominator of all these verses is that the person saying them is declaring his wish to orient his consciousness toward the divine dimension of eating rather than its worldly, material, aspects. As such, these verses do not constitute a thematic interruption between the rinsing of the fingertips and the recitation of Grace.
Translated and adapted by Moshe-Yaakov Wisnefsky from Shaar HaMitzvot, Ekev; subsequently published in "Apples From the Orchard." available at Kabbala Online Shop]
Reprinted with permission from Chabad of California. Copyright 2004 by Chabad of California, Inc. All rights reserved, including the right to reproduce this work or portions thereof, in any form, without permission, in writing, from Chabad of California, Inc.