Why is it important to write clearly and professionally?
In business writing, your message should be so clear that it is not subject to different interpretations (unless that is your intention). Writing clearly ensures that your message is conveyed in the way you intend it.
In your message, you need to convey the correct tone, be it warm, friendly, firm, stern, etc. Being mindful of writing professionally will help you to keep your message respectful, regardless of the tone you want to convey.