I wanted to understand the meaning of this sentence properly

In this case turn about does not mean turn and face in the opposite direction it means circle around the point mentioned, in this specific case the person's calling or vocation. You can tell this from the comparison with a potter's wheel

This is probably the origin of the term turn about meaning turn and face in the opposite direction as that means turn about the centre line of your body and is mainly used by the army to drill soldiers.

I interpret the meaning of the sentence (which is archaic and also a little fanciful in its style) as "Do not have long-term goals or ambitions for your trade or profession, do in it what is required of you on a day-to-day basis and as ideas come to you but always bear in mind the central nature of the trade or profession"

Either this is a very old piece of writing, or it is a prescription for a philosophical or religious way of life rather than a guide to business, or it is both. It sounds to me rather like part of the instructions for the Yogic "Path of the Householder" where the Yogi lives "in but not of the world".

What book does it come from?

Edit after posting I've just seen the comment by @weathervane which was written while I was writing this answer and the suggestion that calling means the person's true calling or higher calling rather than vocation is very compelling. This would mean that the following of the trade, profession, or even casual labouring work should be secondary to the true calling which should always be the person's primary focus.