It is only to the vain that all is vanity - The author of the statement is of the view that it is only useless if one says that all is vanity. The second sentence adjacent statement in the question should support this.
1. Option a is tricky in that it restates more or less that "all is vanity" but does not negate it that it is only to the vain - all is arrogance only to those who have never been proud of themselves.
2. Option b is right in the sense that all is deception only to those who has never been sincere with themselves.

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