פּירוש אויף מלכים ב 2:10

You have made a difficult request. It is impossible [for me] to give you more than I possess.⁵According to Rashi, Elisha apparently asked for a double portion of Eliyahu’s spirit. Alternatively, Elisha requested to attain two thirds of Eliyahu’s spirit and for all other prophets together to attain one third. -Radak Or, Elisha requested double the spirit of any other prophet.—Ralbag

You asked something difficult ~ It would have been enough for you if you had asked a just part of my spirit, or even half, but asking for it twice is something difficult, and even though [it is difficult] if you have the spiritual strength to see me as I am taken from you then I will know that from God this will happen, and so you will have what you asked.

If you will witness my departure from you. Then I will be able to do more and more.⁶I.e., if you are spiritually elevated enough to observe my ascent, it would be an indication that your request would be granted.

It will be so for you, and if not, it will not be. That I am unable [to do so].