"they Whatever can make life truly happy is absolutely good i..." — Seneca quote meaning

they Whatever can make life truly happy is absolutely good in its own right because it cannot be warped into evil From whence then comes error In that while all men wish for a happy life they mistake the means for the thing itself and while they fancy themselves in pursuit of it they are flying from it for when the sum of happiness consists in solid tranquillity and an unembarrassed confidence therein they are ever collecting causes of disquiet and not only carry burthens but drag them painfully along through the rugged and deceitful path of life so that they still withdraw themselves from the good effect proposed the more pains they take the more business they have upon their hands instead of advancing they are retrograde and as it happens in a labyrinth their very speed puzzles and confounds them