The next two letters (24-25) were actually written by R’ Salanter’s original Mussar teacher, the great and holy R’ Yoseph Zundel of Salant.
(In fact, we’ve already come to the end of R’ Salanter’s letters per se. Their editor and publisher, R’ Isaac Blazer, apparently decided to include other works so as to “round out” the book. We came upon the first instance of that in the previous “letter” which was actually a homily, as we indicated there; these letters by R’ Yoseph Zundel are another instance of it; the next three “letters” (26-28) are actually lectures that R’ Salanter delivered in his yeshiva; “letter” 29 was in fact a separate work included in a Torah journal that R’ Salanter published; and the final entry (30) is a major Mussar work unto itself which we’d be that much poorer for not knowing of if it weren’t included here.)
R’ Yoseph Zundel wrote his letters to his (adult) son who was selflessly and nobly helping the ill and doing other acts of service to those in need. The young man’s efforts were apparently thwarted and he came to be dismayed so he asked his father for encouragement and insight, and that’s the makeup of these two letters. As each one of us has had his wishes stymied one time or another (whether we were trying to do something as lofty as this or not) these letters are useful to us all. We’ll combine them since there are some repetitions and overlaps within them.
R’ Yoseph Zundel reminded his son not to fall into the trap of taking credit himself for what he might succeed at in his important mission, but to always seek G-d’s own intercedence and rely on it alone. The best way to do that and to instill it in your heart is to constantly repeat certain verses to yourself that make just that point (see Psalms 27:14 and 25:15, Deuteronomy 31:6, and many others.) And it would do you well to always recall the fact that G-d interacts with you each and every moment — even if you disagree with His decisions.
If your intentions are thwarted despite that, then know that while the reasons why that’s so may be hidden from us all, they can often be tied to our own personal failings rather than mere “circumstances”. In any event it would be best to accept all failings with grace and love. And one should never regret any good he meant to do despite his failings or grow discouraged, and he or she should rest assured in the knowledge that they will be rewarded for all their good works (despite the outcomes).
And lastly we should all learn to accept G-d’s decisions and decrees, as well as to catch sight of all the goodness He bestows upon us despite everything we do or don’t do.