Twichell took his job as chaplain seriously. He expresses moral indignation about the abuse of alcohol (he was a teetotaler), use of profanity, discord among the troops, the execution of deserters, and tension between Protestants and Catholics. He tried his best to find common ground with Catholics, hoping that his example would impress them spiritually. Though never fully approving of Catholics, he did develop a fast friendship with a Catholic chaplain, Father O'Hagan, and grew to appreciate some elements of Catholic faith. His familiarity with Catholics mitigated the natural suspicion and hostility he had inherited from his background—and set him apart from most of his fellow Protestants, especially after the war.
He is no distant, cold observer. He admits to depression and loneliness and homesickness. He expresses affection for his faithful horse, deep concern for family back home, and frustration when he does not receive letters. His father's sudden death in 1863 dealt him a severe blow. "O, my Father! My Father, where are thou? Is it I, or is it he that is lost? … Now with unutterable yearning I grope round the shadowed world after him, and find nothing but fresh grave … . I shall never write 'Dear Father' again—never." Is the style grandiloquent, grating on 21st-century sensibilities? Yes, but the emotion is real, the sense of loss universal.
Twichell believed that the Union cause was right. The North's commitment to preserve the union and abolish slavery was noble, even redemptive. He condemns the South, vilifies Copperheads (northern Democrats who opposed the war and advocated withdrawal), and extols the "magnificence" of the Union army. Yet there is a Lincolnesque quality to his writing, too. He speaks of an "Eternal Plan" that no one could ultimately fathom. On occasion he admits doubt:. "I pray continually that God in pitying mercy will end these dreadful times. I often am inclined to think that, after all, liberty [may] cost too much. If you could see what I have seen you would be thus tempted also." At such times only faith sustains him. "If I had no faith in God, and did not feel that the plan, the plan, is unfolding in ways of His appointment, I should go crazy. I thought yesterday that I should not much care if I had done with earth, so full of violence."
Both a revivalist and a social reformer, Twichell would find it hard to understand why anyone might imagine that those commitments were antithetical. He believed that the war presented a rare opportunity to preach Christ: "I do not know that I shall ever again be placed where I can preach the Gospel with such an advantage as here and certainly I shall never be placed where it is more needed." He endorsed the cause of temperance, favored strict Sabbath observance, and, above all, opposed slavery, which was an evil that had to be stamped out, no matter what the price:






