Adam Clarke on Luke 9:25

Lose himself - That is, his life or soul. See the parallel places, Mat 16:25 (note); Mar 8:35 (note), and especially the note on the former.

Or be cast away? - Or receive spiritual damage η ζημιωθεις. I have added the word spiritual here, which I conceive to be necessarily implied. Because, if a man received only temporal damage in some respect or other, yet gaining the whole world must amply compensate him. But if he should receive spiritual damage - hurt to his soul in the smallest degree, the possession of the universe could not indemnify him. Earthly goods may repair earthly losses, but they cannot repair any breach that may be made in the peace or holiness of the soul. See on Mat 16:26 (note).