Jesus follows the grain-of-wheat image by saying that the one who loves his life loses it, while the one who 'hates' his life in this world will keep it for eternal life.
The language is deliberately severe, but it should be heard within biblical patterns of comparative loyalty.
Hebrew and Jewish idiom can use 'love' and 'hate' to express preference, allegiance, or relative priority as well as emotion. Genesis' family narratives and later biblical usage provide examples where one person is 'hated' in the sense of being loved less or placed second. Jesus is not commanding psychological self-loathing or contempt for human life. The contrast concerns which life and loyalty governs when discipleship becomes costly.
The idiom prevents a destructive reading while preserving the radical demand. Jesus is not teaching that bodily life is worthless.
He is saying that self-preservation cannot be the highest allegiance. In the immediate context, that principle follows his own movement toward death and becomes the pattern for those who serve and follow him.