The story is told of an ascetic who iso- lated himself in his room for many years, studying Torah and praying.
His most basic necessities were passed to him through a slot in the door.
Over time, he began to hear sounds near his door, which he assumed were made by Jews who were pushing forward to hear and be moved by his Torah study and divine service.
As a result of this assumption, he was energized like a lion during his prayers, and he would pray with a loud voice that could be heard from afar.
After twenty years passed, he opened the door and discovered a family of cats that resided outside his door.
He realized that he had studied and prayed for twenty years for the benefit of a family of cats.
It is possible for a person to study and pray for his entire life and not serve God at all, but rather he serves himself.
Rabbi Adin Steinsaltz