'Commandeth' is the old form of the third person singular in the present simple. 'He Commandeth' It dates back to the middle English language of the 12th to 15th century. The use of -eth in spoken English was lost after the 15th century. Today we use 'He commands'. Although you will still find it in older versions of The Bible.'

I shalt thee attencion commandeth:

Yes, it is in ancient English. No one says commandeth anymore. That looks like Biblical talk....as in "such sayeth the Lord". Now I wonder if anyone used to talk like that anyway. Maybe it was only in books. Now, I am curious, too. We need some historical expert to really answer this question. Whatever, I'm glad we don't talk like that anymore as it sounds so silly.