Psalm 19:12-14: In Your Presence
Who understands [his] transgressions? Pardon me of [my] unknown faults. Also keep back your servant from insolent [sins]; [do] not [let them] rule over me. Then I will be innocent and free from great transgression. Let the words of my mouth and the meditation of my heart be pleasing in your presence, ʏʜᴡʜ, my rock fortress and my redeemer. — Psalm 19:12-14 [Heb. verses 13-15] my translation
Having sung about the supreme value of the word of ʏʜᴡʜ, and the rewards that it offers, David deals with the matter of personal sin and temptation, which threatens to derail him from these lofty delights and benefits.
Who understands [his] transgressions? Pardon me of [my] unknown faults. — Psalm 19:12 [Heb. verse 13] my translation
As fallen creatures, we have been so greatly tainted with sin and evil desires, that even those who sincerely seek to follow ʏʜᴡʜ, and who are indwelt by his Spirit, cannot fully grasp all the ways that we transgress in our hearts and in our behavior. The word here for transgressions is שְׁגִיאוֹת (shᵉgị-ʾōt), a noun which is used only once in the Hebrew scriptures. Nevertheless, it appears to be related to the roots שׁגג ("to make a mistake inadvertently, unwittingly", or "to go astray") and שׁגה ("to stray [of sheep])" or "to do wrong inadvertantly, unintentionally"). Such sins of ignorance, though not proceeding from a rebellious heart, would nonetheless be an obstacle to us enjoying blessing from God. Therefore, it is necessary that such sins be recognized in a general way, as we look to God to pardon or forgive us for our "unknown faults", while also looking to him to instruct us over time and make clear to us what is the right path.
Also keep back your servant from insolent [sins]; [do] not [let them] rule over me. Then I will be innocent and free from great transgression. — Psalm 19:13 [Heb. verse 14] my translation
Another potential obstacle to enjoying the rewards and delight of the law of ʏʜᴡʜ is the danger of falling into bold or "insolent" sin which is a danger threatening to completely derail us from following ʏʜᴡʜ. The word זֵד (zēd) here means "insolent" or "presumptuous". While here the word is used to refer to a class of sins, a helpful cross reference is Proverbs 21:24, where זֵד is used to refer to an arrogant person. He is described as the "haughty-one" who acts "with-overflowing-of pride" (ESV interlinear).
Here in Psalm 19, the "insolent" or "presumptuous" sins are those committed boldly in opposition to what we clearly know is the will of God, and so they are necessarily a manifestation of pride. Such sins are characteristic of damned souls who openly reject and despise the word of ʏʜᴡʜ. But they are also a danger for true believers, as one who commits such a sin cannot continue to follow and commune with God, while he remains in a stance of rebellion against God.
King David himself fell into such a sin, in the incident with Bathsheba. In his case, he had the resources to execute a cover up, and consequently he spent around a year of his life in utter misery, inwardly writhing under the weight of his guilt and the convicting work of the Holy Spirit, while outwardly maintaining a facade of righteousness before his subjects. Fortunately the prophet Nathan, in a very courageous act, confronted David with his sin, and David repented and found restoration and inner healing, though David still suffered many griefs in the fallout from his sin.
These "insolent" sins will "rule over" a person, dominating his life, and are called "great transgression". And so it greatly desired to be "innocent" and "free" from them. But we are not sufficient in and of ourselves to resist such temptations. ʏʜᴡʜ must "keep [us] back" from falling into them — we need God's active spiritual protection, working in our hearts and in our circumstances. This is a great motivation to pray — we need to be on our knees each morning, begging God to help us navigate the spiritual dangers of the day ahead.
Let the words of my mouth and the meditation of my heart be pleasing in your presence, ʏʜᴡʜ, my rock fortress and my redeemer. — Psalm 19:14 [Heb. verse 15] my translation
The psalm comes to a climax with an expression of the psalmist's highest desire, a longing to abide close to ʏʜᴡʜ and to be pleasing to him. The word לְפָנֶ֑יךָ (lᵉfā-ney-khā) is generally translated "in your sight" (for example, NIV, NASB, KJV) but is literally "before your face", and has the idea of being in someone's presence, for example, when Moses casts down his staff in the presence of Pharoah. ʏʜᴡʜ is David's צוּר — his rock — used metaphorically as a place of protection, safety and refuge. And ʏʜᴡʜ is his redeemer, the one who delivered him or bought him back out of his distress and trouble. And so he prays for God's help, that his words and meditation would be pleasing to ʏʜᴡʜ, suitable for in his presence. "Meditation" in Scripture is not an emptying of the mind, as in some eastern religions, but refers to the inward thought processes. And our words are ideally a wholesome reflection of a healthy inward state.
 HALOT. The word is frequently translated "errors" in English translations (for example, NASB, NIV, ESV, KJV). ISV gives "mistake" and CPDV gives "trangression".
 See Psalm 51.
 There is some question here on whether to translate מִפֶּשַׁע רָב (miph-phe-shaʿ rov) as indefinite or definite, that is, as "great transgression" or "the great transgression", the latter perhaps being a reference to apostasy. The general rule on definite vs. indefinite is that "A word that does not refer to a particular thing is indefinite. A word is indefinite if it is not a proper noun, does not have a pronominal suffix, and does not have the article (Williams §82a) and is not in the construct state (Williams §82b). However, Williams does indicate that the article is sometimes deliberately left off in poetry, to emulate archiac style "before the development of the article" though this seems to be only referring to cases where the words are "normally written with the article before each noun" (Williams §82e). Here are singular instances without the article: Exodus 34:7; Numbers 14:18; Isaiah 59:20. A singular use with the article is found in Daniel 9:24.
 The word translated "free" here is נקה, which in this case means "to be without blame" (HALOT). The general idea of the word is to be free from something.
 Exodus 7:10; Cf. Exodus 34:34; 1 Samuel 17:57.
 Regarding גֹאֲלִי (gō-ʿālị): HALOT gives "to claim for oneself, to redeem (God)" for this instance, under the category "to reclaim as one's own". Cf. Exodus 6:6.
 Regarding הֶגְיוֹן (heg-yōn): HALOT gives "meditation" for this instance. Apparently the root is הגה, suggesting the idea here of the inner speech or mutterings of the heart.