Jesus is tackling sinful pride in his disciples which is leading them to mistreat others whom he would value and love. So he speaks firmly to the twelve. They have to change their mindset to one of humility and self-sacrifice, like his own. If they cause fragile believers to stumble in their faith, he will come down hard on them. If they let their strength become arrogance, they are in danger of running into Hell. So they must cut it from their lives and, instead, devote themselves to serving others. That is the sacrifice which expresses true gratitude to God for his salvation and which, therefore, brings eternal reward.
And here is a short talk based on the same passage: He Changed The World (Episode 37)