We are a commune of inquiring, skeptical, politically centrist, capitalist, anglophile, traditionalist New England Yankee humans, humanoids, and animals with many interests beyond and above politics. Each of us has had a high-school education (or GED), but all had ADD so didn't pay attention very well, especially the dogs. Each one of us does "try my best to be just like I am," and none of us enjoys working for others, including for Maggie, from whom we receive neither a nickel nor a dime. Freedom from nags, cranks, government, do-gooders, control-freaks and idiots is all that we ask for.
Against you and you only have I sinned and done what is evil in your sight--that's true, no excuses, contrition. The world would be a better place to live if we all acknowledged our shortcomings aloud before our Lord.
Your Lectionary's practice of dropping the introductory verses is especially egregious here - the Jewish source tells us two important and seemingly contradictory things:
1. For the choirleader. A Psalm of David.
2. When Nathan the prophet came unto him, after he had gone in to Bath-sheba.
So this is a public prayer - about a very private, shameful, sin with potentially explosive political repurcussions. The prophet himself connects this sin to the future scandals and revolts that will rock the kingdom.
(It is worth noting that Nathan is not hounded, imprisoned or killed... as in most monarchies, and as done to Isaiah and Elijah by evil kings... unlike Saul, David immediately admits his sin.... Like his ancestor Judah, G-d chooses David for leadership not because of otherworldly perfection or pure hands, but for his willingness to repent and admit the truth.)
From here i will use your Lectionary's verse numbering. The translation takes liberties and is simply innacurate in some places.
1. 'Steadfast' is a creation of the translator:
Pardon/be gracious with me in Your lovingkindess, in Your great mercy erase (literally "rub off") my transgressions.
2. Scrub, launder me of my iniquity, and purify me of my errors.
There are 3 words for sin in Hebrew.
Verse 1 uses the word for intentional sin=transgression.
Verse 2 then mentions sins of moral lapse, poor character, or bad influence (iniquity) and then unintended "errors".
The speaker is searching out their motivations...
These 3 words aee.juxtaposed in parallel strophes of the next verses.
6. 'Inward being' is just "the plastered over places" and 'secret heart' is "what is stoppered/sealed away"... the flowery generalizations are especially grating in the context of this psalm's unblinking honesty.
7. 'Purge' sounds like a medical treatment... nobody ate or burned it... the hyssop twig (symbol of humility and perseverance) was used to sprinkle purifying water on the unclean.
The rest is translated OK.
10. Create in me a pure heart, Almighty, and renew in me a true/centered/well-founded spirit.
...more good stuff in the remaining verses not quoted...