Talmud Shabbat 104a
It was stated above, Rabbi CHisda said: The mem and the samek which were in the Tables stood [there] by a miracle. R. Hisda also said: The writing of the Tables could be read from within and without, e.g., nebub [hollow] would be read buban;-behar [in the mountain] [as] rahab; saru [they departed] [as] waras. The Rabbis told R. Joshua ben Levi: Children have come to the Bet Hamidrash and said things the like of which was not said even in the days of Joshua the son of Nun. [Thus:] alef Bet [means] ‘learn wisdom [alef Binah]; Gimmel Dalet, show kindness to the Poor [Gemol Dallim]. Why is the foot of the Gimmel stretched toward the Dalet? Because it is fitting for the benevolent to run after [seek out] the poor. And why is the roof of the Dalet stretched out toward the Gimmel? Because he [the poor] must make himself available to him. And why is the face of the Dalet turned away from the Gimmel? Because he must give him [help] in secret, lest he be ashamed of him. He, Waw, that is the Name of the Holy One, blessed be He; Zayyin, Het, Tet, Yod, Kaf, Lamed: [this sequence teaches,] and if thou doest thus, the Holy One, blessed be He, will sustain [Zan] thee, be gracious [Hen] unto thee, show goodness [metib] to thee, give thee a heritage [Yerushah], and bind a crown [Keter] on thee in the world to come. The open Mem and the closed Mem [denote] open teaching [Ma'amar] and closed [esoteric] teaching. The bent Nun and the straight Nun: the faithful [Ne'eman] if bent [humble], [will ultimately be] the faithful, straightened. Samek, ‘ayyin: support [Semak] the poor [‘aniyyim]. Another interpretation: devise [‘aseh] mnemonics [Simanin] in the Torah and [thus] acquire [memorize] it. The bent pe and the straight pe [intimate] an open mouth [peh], a closed mouth. A bent tzadde and a straight tzadde: the righteous [tzaddik] is bent [in this world]; the righteous is straightened [in the next world]. But that is identical with the faithful bent [and] the faithful straightened?-The Writ added humility to his humility; hence [we learn that] the Torah was given under great submissiveness. Kuf [stands for] Kadosh [holy]; Resh [for] Rasha’ [wicked]: why is the face of the Kuf averted from, the Resh? The Holy One, blessed be He, said: I cannot look at the wicked. And why is the crown of the Kuf turned toward the Resh? The Holy One, blessed be He, saith: If he repents, I will bind a crown on him like Mine. And why is the foot of the Kuf suspended? [To show] that if he repents, he can enter and be brought in [to God's favour] through this [opening]. This supports Resh Lakish, for Resh Lakish said: What is meant by, Surely he scorneth the scorners, But he giveth grace unto the lowly? If one comes to defile himself, he is given an opening; if one comes to cleanse himself, he is helped. SHin [stands for] SHeker [falsehood]; Tav [for] emet [truth]: why are the letters of Sheker close together, whilst those of ‘emet are far apart? Falsehood is frequent, truth is rare. And why does falsehood [stand] on one foot, whilst truth has a brick-like foundation? Truth can stand, falsehood cannot stand.