the most important difference between the third eye and the dasam duar is naam.
opening the third eye (brow chakra, eye of knowledge, etc) is the highest spiritual state you can reach without naam. when the third eye opens, people get spiritual powers, ridhi sidhi, telling the future, things like this. but the opening of the third eye is not enlightenment, it's one of the last stage BEFORE enlightenment. a lot of yogis, and spiritual teachers can teach their students how to open the third eye, but they can't get any farther. the third eye, along with the lower chakras, are accessible to anyone through yoga or meditations. but the tenth gate is hidden, closed, and can only be opened with guru sahib blesses us with naam.
ਮਾਰੂ ਮਹਲਾ ੫ ॥
Maaroo, Fifth Mehl:
ਬਾਹਰਿ ਢੂਢਨ ਤੇ ਛੂਟਿ ਪਰੇ ਗੁਰਿ ਘਰ ਹੀ ਮਾਹਿ ਦਿਖਾਇਆ ਥਾ ॥
I have quit searching outside; the Guru has shown me that God is within the home of my own heart.
ਅਨਭਉ ਅਚਰਜ ਰੂਪੁ ਪ੍ਰਭ ਪੇਖਿਆ ਮੇਰਾ ਮਨੁ ਛੋਡਿ ਨ ਕਤਹੂ ਜਾਇਆ ਥਾ ॥੧॥
I have seen God, fearless, of wondrous beauty; my mind shall never leave Him to go anywhere else. ||1||
ਮਾਨਕੁ ਪਾਇਓ ਰੇ ਪਾਇਓ ਹਰਿ ਪੂਰਾ ਪਾਇਆ ਥਾ ॥
I have found the jewel; I have found the Perfect Lord.
ਮੋਲਿ ਅਮੋਲੁ ਨ ਪਾਇਆ ਜਾਈ ਕਰਿ ਕਿਰਪਾ ਗੁਰੂ ਦਿਵਾਇਆ ਥਾ ॥੧॥ ਰਹਾਉ ॥
The invaluable value cannot be obtained; in His Mercy, the Guru bestows it. ||1||Pause||
ਅਦਿਸਟੁ ਅਗੋਚਰੁ ਪਾਰਬ੍ਰਹਮੁ ਮਿਲਿ ਸਾਧੂ ਅਕਥੁ ਕਥਾਇਆ ਥਾ ॥
The Supreme Lord God is imperceptible and unfathomable; meeting the Holy Saint, I speak the Unspoken Speech.
ਅਨਹਦ ਸਬਦੁ ਦਸਮ ਦੁਆਰਿ ਵਜਿਓ ਤਹ ਅੰਮ੍ਰਿਤ ਨਾਮੁ ਚੁਆਇਆ ਥਾ ॥੨॥
The unstruck sound current of the Shabad vibrates and resounds in the Tenth Gate; the Ambrosial Naam trickles down there. ||2||
ਤੋਟਿ ਨਾਹੀ ਮਨਿ ਤ੍ਰਿਸਨਾ ਬੂਝੀ ਅਖੁਟ ਭੰਡਾਰ ਸਮਾਇਆ ਥਾ ॥
I lack nothing; the thirsty desires of my mind are satisfied. The inexhaustible treasure has entered into my being.
ਚਰਣ ਚਰਣ ਚਰਣ ਗੁਰ ਸੇਵੇ ਅਘੜੁ ਘੜਿਓ ਰਸੁ ਪਾਇਆ ਥਾ ॥੩॥
I serve the feet, the feet, the feet of the Guru, and manage the unmanageable. I have found the juice, the sublime essence. ||3||
ਸਹਜੇ ਆਵਾ ਸਹਜੇ ਜਾਵਾ ਸਹਜੇ ਮਨੁ ਖੇਲਾਇਆ ਥਾ ॥
Intuitively I come, and intuitively I go; my mind intuitively plays.
ਕਹੁ ਨਾਨਕ ਭਰਮੁ ਗੁਰਿ ਖੋਇਆ ਤਾ ਹਰਿ ਮਹਲੀ ਮਹਲੁ ਪਾਇਆ ਥਾ ॥੪॥੩॥੧੨॥
Says Nanak, when the Guru drives out doubt, then the soul-bride enters the Mansion of the Lord's Presence. ||4||3||12||