The Torah’s Ways are Pleasant
The Gemara states that one cannot use a palm shoot to fulfill the mitzvah of lulav, because although its stems can be tied and this would fulfill the requirement of kafus, tied up, it is invalid because it is said regarding the Torah its ways are ways of pleasantness, and all its pathways are peace. A palm shoot has thorns that make it difficult to hold, and the Torah would not instruct us to take such a branch on Sukkos.
It is fascinating that the Gemara uses a verse to prove that the ways of the Torah are pleasant. One may have thought that although HaShem is merciful, regarding mitzvah performance one is at times required to undergo suffering to perform the mitzvah. The verse teaches us otherwise. The Torah’s ways are pleasant, and one should not be subject to pain in performing a mitzvah.
The obvious lesson from this Gemara is that if the Torah ensures that one should not feel pain in fulfilling a mitzvah, then certainly a Jew should not cause his friend any pain, as one is required to love his fellow man, and causing someone else pain would be the antithesis of loving a fellow Jew.