Locke is paraphrasing a psalm in which David asks forgiveness. He not only stole Bathsheba from her husband, but ensured he was killed in a coverup. It is often the coverup that does more damage.
The verse paraphrased today is the second half of verse four.
Against you, you only, have I sinnedPsalm 51:4, ESV.
and done what is evil in your sight,
so that you may be justified in your words
and blameless in your judgment.
This is very early modern English: the spelling is correct from the printed text but predates standardization by at least two hundred years, and words such as "thou" and "hehight" (bought) were not archaic. This is best read out loud.
But mercy Lord, O Lord some pitie take,Anne Locke, Medication of a Penitent Sinner.
Withdraw my soule from the deserued hell,
O Lord of glory, for thy glories sake:
That I may saued of thy mercy tell,
And shew how thou, which mercy hast behight
To sighyng sinners, that haue broke thy lawes,
Performest mercy: so as in the sight
Of them that iudge the iustice of thy cause
Thou onely iust be demed, and no moe,
The worldes vniustice wholy to confound:
That damning me to depth of during woe
Iust in thy iudgement shouldest thou be found:
And from deserued flames releuyng me
Iust in thy mercy mayst thou also be.