"Denial," along with being a metaphysical poem, is also a "conceit." A conceit...
George Herbert (1593-1633) was a metaphysical poet who wrote in the 1600s along with John Donne (1572-1631). Metaphysical poems have certain characteristics, one of which is extended sometimes complex conceits that make unusual comparisons between unlike subjects.
"Denial," along with being a metaphysical poem, is also a "conceit." A conceit is a type of lament and as such, it has certain structural characteristics. When you add the characteristics of metaphysical poetry to those of a conceit, it is possible to understand this otherwise elusive modernistic sounding poem.
The six stanzas are written in a fixed pattern of meters. Though each line is iambic (da DA), the three lines of each stanza are in a descending pattern: the first line is hexameter (six feet), the second is pentameter (five feet), the third is tetrameter (four feet) with a final line of four syllables, "Dis-con-ten-ted."
A complaint is a love lament characterized by the poetic apostrophes of personal appeal to some absent person or power: "O that thou"; "O cheer and tune". Complaints open by complaining against a loved one but become complex because they turn upon (are thematically aimed at) greater issues that are expressed after the initial complaint against love. The conclusion may be one that indicates an ongoing process or a deliberation over decisions to be made.
Putting it together to understand "Denial," the overarching metaphysical conceit in the opening love complaint compares the duality of silence/hearing of a loved one to God's silent, unhearing ears. This conceit begins in the first stanza and carries through the final lament and end stanza, while other conceits add complexity. A second conceit compares thoughts to archery and the wounds of arrows. A third conceit compares the heart (emotion and soul) to a tuneless, unstrung instrument.
The greater issue the complaint turns upon is the metaphysical one of God's silent attitude toward human suffering. The conclusion of the complaint reflects an ongoing with the poet now supplicating God to hear and grant his request that he be brought out of suffering and back into spiritual harmony.
Now that the metaphysical elements and the complaint-lament elements have been identified, the poem should be more clear. The complaint persona is assumed to be the poet's own voice.
In "Denial," the poet complains that his love appeals have fallen on "silent" ears that reject his avowals of love. His heart is broken as is "his verse" (which accounts for the "broken" descending metrical pattern). His feelings and thoughts have fallen into disorder with each, like badly aimed arrows, going their own random, disordered way.
In a personification of his thoughts, his thoughts say it is better than to continually pray for relief, since pleas fall on "unhearing" ears. The poet's lament to God occupies the last three stanzas, with the third conceit of the heart as a tuneless instrument. The poem ends with the apostrophe "O cheer and tune my heartless breast."
The conclusion shows him awaiting God's hearing so that his "mind may chime" and his broken rhyme may mend. While the love complaint begins the poem, the larger metaphysical idea is God's relationship with humans and the need for spiritual harmony, with hearts are attuned to God.
O cheer and tune my heartless breast,
Defer no time;
That so thy favors granting my request,
They and my mind may chime,
And mend my rhyme.