मया प्रसन्नेन तवार्जुनेदं रूपं परं दर्शितमात्मयोगात्।तेजोमयं विश्वमनन्तमाद्यं यन्मे त्वदन्येन न दृष्टपूर्वम्॥
mayā prasannena tavārjunedaṃrūpaṃ paraṃ darśitam ātma-yogāttejo-mayaṃ viśvam anantam ādyaṃyan me tvad anyena na dṛṣṭa-pūrvam
Word by word
The verse says
Krishna said: By my grace, Arjuna, and by my own power, I have shown you this highest form — made of light, universal, endless, the first — which nobody but you has ever seen.
In plain words
Mayā prasannena — by me, being pleased. Graciously.
He explains why it happened, and the reason is not Arjuna's merit.
And then: nobody else has seen this. The vision was not available and then given. It was never available.
Where you've felt this · at work
A master craftsman lets an apprentice watch him do the one part of the job he has never let anybody watch. Afterwards he says, plainly, that he has not shown that to anybody. He is not boasting. He is telling the apprentice what just happened, because otherwise it might be taken for an ordinary afternoon.
Going deeper
Being told the significance of what just happened to you is sometimes necessary, and that is what this verse is for.
Arjuna has been inside the experience and in no position to assess it. Krishna tells him three things: it came by grace rather than achievement, it was produced by his own power, and nobody else has ever seen it. None of that was available to Arjuna from the inside.
The first point matters most and the chapter will press it twice more in the verses that follow.
For a reader, the usable part is about how spiritual experience gets evaluated. People who have had something remarkable happen tend to look for what they did to deserve it, and people who have not tend to look for what they failed to do. The verse rules out both accounts in the same sentence.