What this really means is that those who think of themselves as "first" (worthy) are following ego, instead of God and Jesus, and thus will be counted last among all.
Those who have no thought of self, but who love unconditionally and give generously of themselves are putting themselves as "last" (a humble servant), and thus will be counted first, because they are doing as God and Jesus would do through love.
Ego is the master of this world, and all too often those who think highly of themselves are actually following ego instead of Jesus and God. Ego is the "false self" that must die before we can gain everlasting life.
When all attachments to ego are gone, the true self can awaken. When that happens, consciousness no longer depends upon the physical brain, but resides instead in the true self (soul, Holy Ghost, child of God), within. I have experienced this once, 41 years ago, and long to find it again permanently.
But Jesus said, "ask and you will receive." I'm not there, yet. So, I practice being as humble as a beggar. And for me, that takes a lot of practice.