In Mark 16:14, Jesus Christ appeared to the disciples and rebuked them for two reasons:
1. For being hard-hearted
2. For lacking faith
How can someone be able to harden his heart and lack faith? Faith comes from hearing the word of God (Romans 10:17). If you hear the word of God and do not take it as it is, then you have hardened your heart and because of that you will be rebuked.
Jesus did not rebuke them for hating their bodies or walking with sinners, not even for their phyiscial actions. Jesus rebuked them for their lack of faith and hardening of their hearts.
Why does Jesus rebuke his disciples for being hard-hearted and lacking faith instead of for their sinful behavior?