Lose himself - That is, his life or soul. See the parallel places, Matthew 16:25 (note); Mark 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 Matthew 16:26 (note).

For what is a man advantaged if he gain the whole world,.... Or what profit will it be unto him? all the honours, riches, and enjoyments of it will be of no use and service to him if he himself is lost:

and lose himself; or his own soul; for he that loses his soul, which is his better and immortal part, loses himself:

or be cast away: finally, and eternally, or "suffer loss" of eternal happiness and glory; that is, perishes, and is destroyed with an everlasting destruction; See Gill on Matthew 16:26.

Gain (κερδήσας)

A merchant's word. Jesus is putting the case as a common-sense question of profit and loss.

Lose (ἀπολέσας)

"When he might have been saved" (Bengel). This word, in classical Greek, is used: 1. Of death in battle or elsewhere. 2. Of laying waste, as a city or heritage. 3. Of losing of life, property, or other objects. As an active verb, to kill or demolish. 4. Of being demoralized, morally abandoned or ruined, as children under bad influences. In New Testament of killing (Matthew 2:13; Matthew 12:14). 5. Of destroying and perishing, not only of human life, but of material and intellectual things (1 Corinthians 1:19; John 6:27; Mark 2:22; 1 Peter 1:7; James 1:11; Hebrews 1:11). 6. Of losing (Matthew 10:6, Matthew 10:42; Luke 15:4, Luke 15:6, Luke 15:8). Of moral abandonment (Luke 15:24, Luke 15:32). 7. Of the doom of the impenitent (Matthew 10:28; Luke 13:3; John 3:15; John 10:28; 2 Peter 3:9; Romans 2:12.

Cast away (ζημιωθείς)

Another business term. The word means to fine, amerce, mulct; to punish by exacting forfeit. Hence Rev., correctly, forfeit his own self. See on win your souls, Luke 21:19. Also on Matthew 16:26.

For what is a man advantaged, if he gain the whole world, and lose himself, or be cast away?

9:22-27 The Son of man must suffer many things, etc. For the first announcement to his disciples of his death, and the discourse, see notes on Mt 16:21-28 Mr 8:31-9:1.

9:18-27 It is an unspeakable comfort that our Lord Jesus is God's Anointed; this signifies that he was both appointed to be the Messiah, and qualified for it. Jesus discourses concerning his own sufferings and death. And so far must his disciples be from thinking how to prevent his sufferings, that they must prepare for their own. We often meet with crosses in the way of duty; and though we must not pull them upon our own heads, yet, when they are laid for us, we must take them up, and carry them after Christ. It is well or ill with us, according as it is well or ill with our souls. The body cannot be happy, if the soul be miserable in the other world; but the soul may be happy, though the body is greatly afflicted and oppressed in this world. We must never be ashamed of Christ and his gospel.