When one begins on his path of teshuvah, Hashem sends a light of holiness that inspires him, and makes his return easy and enjoyable.
Then, Hashem takes away the light and the tests begin. Now he must stand strong by himself. At this phase, a person is tempted to give up. But if he remains strong in his resolve, avodas Hashem will eventually become easy and sweet for him once again.
~ R’ Elimelech Biderman