Behar. Words Hurt

Words Hurt!
Our parsha is the source for the Torah's aversion to abusive speech. Halakha labels this prohibition “Onaat Devarim” – verbal oppression – and it is is articulated by Maimonides in the following manner:
“If you encounter a newly religious person one must not remark: "Remember your former life."
If a convert comes to study Torah, one must not say: "Shall the mouth that ate unclean and forbidden food study Torah which has been given by the Lord?"
If a person has been afflicted with disease and suffering, or if he has buried his children, one must not say the words used by Job's companions in addressing Job: "… what guiltless man has ever perished?" (Job 4:6-7).” (Mishneh Torah, Laws of Transactions 14:13)
Please discuss:
What do each of these cases have in common?
Why should a person not remind a penitent or a convert of his former life?
Why should a person refrain from suggesting that an individual is suffering because of their sins?
What are the friends of this sufferer thinking? Do they intend to heal or to har