Have you ever seen a plastic toy painted to look like gold? On the outside it shines pretty, but on the inside it's still just cheap plastic. That's called a coating: a pretty layer that hides what's underneath.
The Bible compares that to people who speak beautifully, with fervent words, but have a heart full of evil on the inside. It's like a clay pot painted to look like silver.
Think of a classmate who compliments everyone to their face, but talks badly behind their back. Their words are the "coating," but their heart shows the truth. God isn't impressed by outward shine, He looks at what's inside the heart.
Jesus confronted religious people who did this, who looked pretty on the outside but were empty on the inside. He wants us to be the same on the inside as on the outside, without needing a coating to look good.
God doesn't look at the outward shine, He looks at what's inside the heart.