When once upon the head it’s evergreen

And altogether used in righteousness,                                                           20

Where blessed bliss, and blissful peace is seen

And where no jar, nor brawler hath access.

Oh! Blessed crown what hold the breadth of all

The state of happiness in heaven’s hall.

Notes:

Here, Taylor places the reception of the crown in the world to come, “In heaven’s hall”.  (line 24)

The nature of this crown: When it given, it is perpetual in its glory, “When once upon the head it’s evergreen.” This relates to Augustine’s four-fold state of the human will:

“Augustine argued that there are four states, which are derived from the Scripture, that correspond to the four states of man in relation to sin: (a) able to sin, able not to sin (posse peccare, posse non peccare); (b) not able not to sin (non posse non peccare); (c) able not to sin (posse non peccare); and (d) unable to sin (non posse peccare). The first state corresponds to the state of man in innocency, before the Fall; the second the state of the natural man after the Fall; the third the state of the regenerate man; and the fourth the glorified man.” https://www.monergism.com/thethreshold/articles/onsite/augustinewill.html

To be in heaven is to not be able to sin. Incidentally, one might ask how one could be free and be able to not sin. You can think of freedom in many ways. One way to understand freedom is freedom from, here freedom from sin. God is the more free than any creature and God cannot sin. When sin is understood as a limitation, than freedom, than the choice to sin is not freedom.

The crown, once gained, is not merely eternal but it perpetuates righteousness.

Next comes the best line in the poem:

Where blessed bliss, and blissful peace is seen

The rhythm of the line is perfectly regular. Taylor’s use of irregular lines would spoil the effects

Where

                  Blessed

                                    Bliss

And

                                    Blissful

                  Peace

Is seen.

We have the alliteration on B (with a matching P).  We have bliss, noun; and blissful (adverb): the same concept in two forms. The line makes a sort of chiasm with Bliss/Blissful in the center. The bliss is blessed and the peace is blissful.

The state of righteousness is a state of evergreen bliss.

The state of peace and bliss is marked by what is not present:

And where no jar, nor brawler hath access.

Jar does not mean the container; think, “jarring”, upsetting.

No one can come here to fight, ‘no brawler”

In the KJV (which would likely have been Taylor’s Bible) twice has Paul rejecting “brawlers:”

1 Timothy 3:2–3 (AV 1873)

² A bishop then must be blameless, the husband of one wife, vigilant, sober, of good behaviour, given to hospitality, apt to teach; ³ not given to wine, no striker, not greedy of filthy lucre; but patient, not a brawler, not covetous;

Titus 3:1–2 (AV 1873)

Put them in mind to be subject to principalities and powers, to obey magistrates, to be ready to every good work, 2 to speak evil of no man, to be no brawlers, but gentle, shewing all meekness unto all men.

If upon earth, brawlers are to be excluded from the church, how much more in heaven.

He then turns to address the crown directly:

Oh! Blessed crown what hold the breadth of all

I am not sure how to understand, “what hold the breadth of all”.  There are two interesting points of this line: First, “what hold”.  I think I should take “what” as a relative pronoun, something along the lines of “that holds”. Second, the crown entails the breadth of all – what? The second question is answerd in the next line

The state of happiness in heaven’s hall.

I would take idea here to be that the crown is sufficient and entails, encompasses all the happiness of heaven. Righteousness thus being a supreme joy of heaven.