The poet examines himself. The argument here comes from faculty psychology which understood a human to be composed of various “faculties”.  (“An obsolete school of psychology based on arbitrarily posited powers or capacities (called faculties) into which the mind was divided, such as will, reason, and instinct, through whose interaction all mental functions and phenomena were supposed to occur.” https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095807861) Here, reason addresses the affections.  It is interesting that he sees reason as the aspect understanding that his affections have gone wrong, because Reformed theologians (of which Taylor would be an example) saw the Fall as affecting reason as well as affections (perhaps it is in reason’s inability to reign in the affections).

Reason knows the affections are misplaced, but is seemingly unable to do more than complain:

My reason rises up, and chides my cup

Bright loveliness itself, what not love thee!

The ordering of images must make the “cup” that which is “lovely”.  The cup does not contain (although the cup itself is to do the action) love. His reason looks to his heart, his soul, which is his “choiceset cabinet,” (https://memoirandremains.com/2022/05/23/edward-taylor-meditation-40-1-was-ever-a-heart-like-mine/) a heart which fails in its task to hold what is of most value. 

He chides his heart, his soul, that it does not love God as the more desirable of all. The cup turns over and spills what it should possess:

Tumbling thy joy, Lord, ore, it rounds me up.

The clause “it rounds me up” closes the concept which begins with “my reason rises up.” The sounds of the alliterative Rs, the “up” to close the clauses. It then makes for an interesting idea, that his reason stands up and knocks over the cup which already tottered.  I must admit though that the final clause “it rounds me up” is obscure. I assume it completes the tumbling joy and hence cup and thus goes with the image of the cup being turned over. 

Shall love’s nest be a thorn bush: not thee bee?

Set hovels up of thorn kids in my heart!

Here again, the concept is obscure to me. It begins easily enough

Shall love’s nest be a thorn bush:

Birds and other animals may make their nest in thorn bushes. For instance, a “firethorn bush” is particularly fit for birds. But one would think that a nest for love would not be set in thorns (thorns being a result of the Fall).  Can this possibly be that love finds itself set in thorns?

Here again an image I cannot make out:

not thee bee? I take “bee” to be phonetic for “be”. That you would not be found in a thorn nest (?). 

And then yet another unclear reference:

Set hovels up of thorn kids in my heart!

Rather than a place for love, I find a thorn nest, a hovel, in my heart. The overarching move seems clear. To put this in more contemporary images, it is an overrun place of drug addicts near a freeway over pass. It is a hovel. 

I do not know what is mean by “thorn kids”. Perhaps it is buds of thorns or the spawn of thorns. 

He comes to his heart, but he does not find love for God. He finds thorns, a hovel, a cup spilled.  And this is a concept which a Christian does know. I should be filled with love for God, but instead I have brambles and thorns, a hovel, shame:

Avant adulterous love, from me depart!