Thomas Merton wrote, in his journal:
"What matters is not spirituality, not religion, not perfection, not success or failure at this or that, but simply God, and freedom in His Spirit. All the rest is pure stupidity."
- Aug. 28, 1965; in A Year with Thomas Merton, Kindle Locations 4109-4110
I agree. With a qualification. If spirituality or success is the fruit of one's monotasked God-relationship, then such God-produced spirituality or success is not stupid.
We could substitute for "stupidity" the word "vanity." All "without God" religious activity and success is in vain because it is purposeless.
OK. But what if there is no God at all? Then all of life, religion, spirituality, success, and so on, is stupid. We could borrow from French atheistic existentialism and substitute for "stupidity" the word "absurd." With God, life is absurd, pointless, purposeless. But God does exist. So living life without God is absurd, pointless, purposeless, vain, and stupid.