Moses said, “I am 120 years old this day. I can no more go out and come, and Hashem has said to me, ‘You shall not cross the Jordan.’”
All his life, Moses aspired to spiritual growth, and reached heights unachieved by any other human being. No further growth was possible, unless he could enter the Holy Land and participate in its unique mitzvos. But since this was denied him, being at a point where he could not grow any more spiritually, life became meaningless, and he willingly accepted death.
Spiritual growth is what gives meaning to life. We should never resign ourselves to a spiritual status quo. There is always more we can do.