If it doesn't sound reasonable, you probably haven't understood it yet. Often because a set of words are more load-bearing than they appear on the surface.

For example, 'achieved enlightenment' may be something that they have had experience with and equate with wisdom. If someone who seems quite wise (at one or two or more levels above yourself) believes in Bhagavad Gita and says their wisdom comes from Bhagavad Gita, you might believe them. Alternatively, you may have identified some thoughts in yourself as 'wise', and then find these thoughts expressed easily and matter of factly by Bhagavad Gita. This is how religions build their credibility: through awe and recognition of common (but noT-too-common) truth.

(So I'll add that) maybe the problem with religion is that people don't understand what the source of wisdom is. They think if they identify a source of one truth, that source is reliable for other truths. So the problem is epistemology, again.

sketerpot... Bhagavad Gita of Hinduism is one such sacred scripture which has universal appeal. Hinduism primarily is never termed a religion... it is a way of life! Bhagavad Gita is not the sole propriety of Hinduism. Anyone belonging to any religion can follow precepts of Bhagavad Gita and reach stage of enlightenment (kaivalya jnana)!

Lord Krishna http://www.godrealized.com/lordkrishna.html ... an avatar of his era (God manifest human form) who gave doctrine of Bhagavad Gita to mankind came about 1500 years earlier to Jesus Christ... about thousand years earlier to Mahavira... the 24th Tirthankara (preceptor) of Jainism! Gautama Buddha followed about 77 years later to Mahavira!

The doctrine of Bhagavad Gita contains truth and only truth. Albert Einstein... a great physicist was an open exponent of teachings of Bhagavad Gita! The prime reason why people failed to understand gist of Bhagavad Gita is... contents of Bhagavad Gita can never be understood literally... it needs reading in between the lines!

RobinZ... putting it other way... normal human beings used their brain 1%! Albert Einstein used his brain 4%! An enlightened one... the knower of Bhagavad Gita used ones brain hundred percent! For assimilating pearls of wisdom contained in Bhagavad Gita... practice of absolute celibacy http://www.godrealized.com/celibacy.html for a minimum period of 12 years in continuation is necessitated!

This 12 years practice of absolute celibacy results in full awakening of kundalini shakti http://www.godrealized.com/glossary/Kundalini-energy.html ... that results in opening of Shahastra Pushpa (thousand petaled Lotus) within our brain that exists behind forehead! The moment this happens... one gained enlightenment... liberated self from cycle of birth and death forever! This is all contained in Bhagavad Gita of Hinduism!

If at any stage one feels offended... rather feels I am trying to teach Hinduism... I shall quit! I am only putting my perspective from Hinduism point of view... the oldest religion of world!