Bg 11.8

na tu mam sakyase drastum
anenaiva sva-caksusa
divyam dadami te caksuh
pasya me yogam aisvaram

Word for word: 
na — never; tu — but; mam — Me; sakyase — are able; drastum — to see; anena — with these; eva — certainly; sva-caksusa — your own eyes; divyam — divine; dadami — I give; te — to you; caksuh — eyes; pasya — see; me — My; yogam aisvaram — inconceivable mystic power.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
But you cannot see Me with your present eyes. Therefore I give you divine eyes. Behold My mystic opulence!

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
A pure devotee does not like to see Krishna in any form except His form with two hands; a devotee must see His universal form by His grace, not with the mind but with spiritual eyes. To see the universal form of Krishna, Arjuna is told not to change his mind but his vision. The universal form of Krishna is not very important; that will be clear in subsequent verses. Yet because Arjuna wanted to see it, the Lord gives him the particular vision required to see that universal form.

Devotees who are correctly situated in a transcendental relationship with Krishna are attracted by loving features, not by a godless display of opulences. The playmates of Krishna, the friends of Krishna and the parents of Krishna never want Krishna to show His opulences. They are so immersed in pure love that they do not even know that Krishna is the Supreme Personality of Godhead. In their loving exchange they forget that Krishna is the Supreme Lord. In the Srimad-Bhagavatam it is stated that the boys who play with Krishna are all highly pious souls, and after many, many births they are able to play with Krishna. Such boys do not know that Krishna is the Supreme Personality of Godhead. They take Him as a personal friend. Therefore Sukadeva Gosvami recites this verse:

ittham satam brahma-sukhanubhutya
dasyam gatanam para-daivatena
mayasritanam nara-darakena
sakam vijahruh krta-punya-punjah

“Here is the Supreme Person, who is considered the impersonal Brahman by great sages, the Supreme Personality of Godhead by devotees, and a product of material nature by ordinary men. Now these boys, who have performed many, many pious activities in their past lives, are playing with that Supreme Personality of Godhead.” (Srimad-Bhagavatam 10.12.11)

The fact is that the devotee is not concerned with seeing the visva-rupa, the universal form, but Arjuna wanted to see it to substantiate Krishna’s statements so that in the future people could understand that Krishna not only theoretically or philosophically presented Himself as the Supreme but actually presented Himself as such to Arjuna. Arjuna must confirm this because Arjuna is the beginning of the parampara system. Those who are actually interested in understanding the Supreme Personality of Godhead, Krishna, and who follow in the footsteps of Arjuna should understand that Krishna not only theoretically presented Himself as the Supreme, but actually revealed Himself as the Supreme.

The Lord gave Arjuna the necessary power to see His universal form because He knew that Arjuna did not particularly want to see it, as we have already explained.