Because the cross is sharp and afflicting, our Lord animates his followers to bear it by the thought of its great and everlasting rewards. The meaning of the verse is this: he who by trying to shun the cross and to escape self-denial would save his life here, will lose it hereafter.
But he who loses his life here for the sake of Christ, either by dying in his cause or by denying and mortifying his lusts out of love for him, he in the life to come shall find his life in the bosom of Christ and in eternal joy.