A Jewish person should not despair from anything, whether in physical matters as it is written (Brachot 10, end of side a) "Even if a sharp sword rests upon a person's neck, he should not refrain himself from the Mercy", or whether in spiritual matters though he has sunk to the place where he has sunk in a matter which our Sages said (Zohar, Section 1, 219:2) that repentance does not help G-d forfend, or that repentance is difficult, or that he sees himself sink in matters of this world, he should not despair of himself to say he cannot separate himself anymore, because there is no despair at all for a Jewish man, and G-d Blessed be He can help with every matter, and the entire building of the Israelite nation came about after total despair that "Abraham and Sarah were old" [Bereishit 18, 11] and "Who is the One Who said to Abraham, 'she would nurse' etc." [Bereishit 21, 7], that it would not occur to a person to yet believe this and even after the promise of the angel. And Sarah the righteous woman knew and believed that G-d Blessed be He can do everything, and even so "she laughed internally", that it was far for her to believe this with her knowledge of Abraham's advanced age..........as it is written in Bereishit Rabbah (Chapter 48, 17) and her own advanced age, and if it had been the will of G-d Blessed be He to remember them he would have remembered them from the outset since reducing the miracle is preferred and He does not perform a miracle where it is not necessary, but the truth is "this has emanated from Hashem" [Psalms 118, 23] that the building of the nation should expressly be after the total despair that no person would believe, even Sarah, that she would yet be remembered, for this is for every Israelite person to believe that he should not despair at all because G-d Blessed be He is always able to help and "is anything beyond Hashem?" [Bereishit 18, 14], and one should not question why Hashem did things this way, and so too of the future salvation it is said (Isaiah 53, 1) "who can believe what we have heard? etc.", and so they said (Sanhedrin 97, end of side a) "the son of David will not come until they despair from the redemption", and therefore it says (Isaiah 51, 2) "Look to Abraham your father, and to Sarah who gave birth to you", that also the basis of your nation's founding (literally, the beginning of your building) was also after despair, and also I found in Tanchuma (commentary on Parshat Va'yeira [16]) on the verse "And Hashem remembered" [Bereishit 21, 1] this same thing, you should study it there, and it will be helpful (translation of vi'ahanyain?).