Midras Mazmur 78:38: Ein Yaakov (Glick Edition), Mekhilta DeRabbi Yishmael & Midrash Tehillim

The former Rabbis were called Soph'rim, because they counted all the letters of the Torah; for they would say the letter Vav of the word Gachon (belly) (Lev. 11, 42) is just one-half the number of the letters contained in the Torah; the word Darosh-Darash (diligently inquired) (Lev. 10, 16) is one-half of the amount of words the Torah contains; the passage V'hisgalach (then he shall be shaven) (Ib. 13, 33) is one-half of the verses of the Torah. In the passage (Ps. 80, 14) The bear out of the forest doth ravage it, the letter Ayin of the word Ya'ar (forest) is one-half the number of the letters of which Psalms consist; the passage (Ib. 78, 38) But He, being merciful forgave the iniquity, is one-half the verses of which the Psalms consist.

Similarly, R. Eliezer b. Yossi expounded (Isaiah 63:9) "In all of their afflictions, He was afflicted," (Ibid. 8) "And He said: 'Surely, they are My people, children who will not lie.'" But did He not know that they would lie? It is, therefore, written "Surely." (i.e., it was surely known to Him (that they would lie.) How, then, are we to understand (Ibid.) "and I will be their salvation"? — He did not save them as men who were destined to anger Him, but as men who (by repentance) were not destined to be faithless to Him forever. And thus is it written (Psalms 78:36-37) "And they deceived Him with their mouths, and with their tongues they lied to Him, and their hearts were not constant with Him, and they were not faithful to His covenant" — in spite of which (Ibid. 38) "But He, being merciful, will forgive transgression," and (Isaiah 6:10) "The heart of this people has become fat, and its ears have become heavy, etc." (— in spite of which) (Ibid.) "if he repents, he will be healed."

And thus do we find with our fathers, that when they stood on Mount Sinai, they sought to steal the Higher Mind, as it is written (Exodus 24:7) "Everything that the L–rd has spoken, we will do and we will hear" — and it (the Higher Mind) was, as it were, "stolen" by them. As it is written (Devarim 5:26) "Would that this heart of theirs were in them to fear Me and to keep all of My mitzvoth all of the days, etc." And if you would say that not all is revealed and known to Him, it is written (Psalms 78:36-37) "And they beguiled Him (only) with their mouths, and (He knew that) their hearts were not constant with Him" — in spite of which (Ibid. 38) "And He was merciful, forgiving sin and not destroying, etc." And it is written (Mishlei 26:23) "As silver dross covering earthenware are lips running (with love) above an evil heart."