Is it permissible for an employer to address his employee with abusive language and treat him harshly? And is this considered a form of arrogance that falls under the scope of the Hadith: "No one who has the weight of a mustard seed of arrogance in his heart will enter Paradise"?

Servants should be treated with gentleness and kindness, and one should avoid harming them with words or deeds. They are human beings with feelings and emotions, and they must be treated with goodness and safeguarded from ill-treatment, for Allah the Almighty says: "And speak to people good words," and "So by mercy from Allah, [O Muhammad], you were lenient with them. And if you had been rude [in speech] and harsh in heart, they would have disbanded from about you." Good character elevates ranks and weighs heavily in the balance. The reason for severity may not be arrogance, but rather a conviction that it is the appropriate approach.