אִֽם־אֶשְׁכָּחֵ֥ךְ יְֽרוּשָׁלִָ֗ם תִּשְׁכַּ֥ח יְמִינִֽי׃
Если я забуду тебя, Иерусалим, пусть моя правая рука забудет ее хитрость.
Akeidat Yitzchak
Man's activities are divided into three categories. 1) Natural, involuntary activities, not subject to teaching, training and memory. Examples are our heartbeat, digestion etc. All these activities are carried on whether man is awake or asleep, none require an act of memory to activate them. When David exclaims "I have forgotten to eat" (Psalms 102,5) this is, of course, merely an exaggeration, expressing the thought that the body no longer functions properly. 2) Activities which result from education, instructions and may be either in agreement with or in opposition to man's natural urges and tendencies. These activities are subject to memory. As we say in Avot chapter 4, there are four categories of students, "some learn easily but forget just as easily." 3) Activities based on man's character traits. Kindness, excitability, generosity etc. are examples of such activities. These latter activities are subject to memory in the early stages of their development, but eventually become ingrained, i.e. like second nature. Once such activities have been fully developed, they are no longer subject to prompting, but occur from force of habit. "If I forget you Jerusalem may I forget my right hand," is an example of such an activity. (Psalms 137,5) Properly attuned, we cannot forget Jerusalem any more than we can forget our right hand. Isaiah 49, 16, has G-d saying "I have inscribed you on My right hand,your walls are always present in My thoughts". Or, (Psalms 77, 10) "Has G-d forgotten to show pity?" Reversal of acquired habits and traits can therefore only be due to one of the following three reasons A) impotence. B) Amnesia C) Change of mind and will. Since categories A and B can obviously not be applied to G-d, David raises the question whether G-d’s change of mind will persist forever. (Psalms 77,9)