Our Gemara on Amud Beis speaks of the responsibility and obligation to fulfill a pledge:


“Once a person said: It is incumbent upon me to bring an offering, it is considered as though the offering is loaded upon his shoulders.”


The idea of a spiritual obligation being felt as a burden upon one’s shoulders is a real phenomenon, but according to Mei Shiloach (Bo) and Sod Yehar (Rosh Hashanah 44), it also changes with time. Just as the Ark was carried on the shoulders of the Levites but miraculously carried itself, so too the burdens of mitzvos are hard at first, but then if you are sincere, God joins you and helps you carry the burden.


As it states, God says, “Open for me an opening the width of the point of a needle, and I will open it wide enough for wagons to pass through.” (Midrash Shir Hashirim 5:22) Once we put in the initial effort, we are not alone in carrying the burden.