By them is thy servant warned - נזהר nizhar, from זהר zahar, to be clear, pellucid. By these laws, testimonies, etc., thy servant is fully instructed; he sees all clearly; and he discerns that in keeping of them there is great reward: every man is wise, holy, and happy, who observes them. All Christian experience confirms this truth. Reader, what says thine?

Moreover

Psalm 119:11 Your word have I hid in my heart, that I might not sin against you.

2 Chronicles 19:10 And what cause soever shall come to you of your brothers that dwell in your cities, between blood and blood, between law and commandment...

Proverbs 6:22,23 When you go, it shall lead you; when you sleep, it shall keep you; and when you wake, it shall talk with you...

Ezekiel 3:17-21 Son of man, I have made you a watchman to the house of Israel: therefore hear the word at my mouth, and give them warning from me...

Ezekiel 33:3-9 If when he sees the sword come on the land, he blow the trumpet, and warn the people...

Matthew 3:7 But when he saw many of the Pharisees and Sadducees come to his baptism, he said to them, O generation of vipers...

Acts 20:31 Therefore watch, and remember, that by the space of three years I ceased not to warn every one night and day with tears.

1 Corinthians 4:14 I write not these things to shame you, but as my beloved sons I warn you.

1 Thessalonians 5:14 Now we exhort you, brothers, warn them that are unruly, comfort the feebleminded, support the weak, be patient toward all men.

Hebrews 11:7 By faith Noah, being warned of God of things not seen as yet, moved with fear, prepared an ark to the saving of his house...

keeping

Proverbs 3:16-18 Length of days is in her right hand; and in her left hand riches and honor...

Proverbs 11:18 The wicked works a deceitful work: but to him that sows righteousness shall be a sure reward.

Proverbs 29:18 Where there is no vision, the people perish: but he that keeps the law, happy is he.

Isaiah 3:10,11 Say you to the righteous, that it shall be well with him: for they shall eat the fruit of their doings...

Matthew 6:4,6,18 That your alms may be in secret: and your Father which sees in secret himself shall reward you openly...

Hebrews 11:6,26 But without faith it is impossible to please him: for he that comes to God must believe that he is...

James 1:25 But whoever looks into the perfect law of liberty, and continues therein, he being not a forgetful hearer, but a doer of the work...

2 John 1:8 Look to yourselves, that we lose not those things which we have worked, but that we receive a full reward.

Revelation 14:13 And I heard a voice from heaven saying to me, Write, Blessed are the dead which die in the Lord from now on: Yes, said the Spirit...

Secret Sins
Now, David, having seen God's law, and having praised it in this Psalm, which I have read in your hearing, he is brought, by reflecting on its excellency, to utter this thought, "Who can understand his errors?" and then to offer this prayer, "Cleanse thou me from secret faults." In the Lateran Council of the Church of Rome, a decree was passed that every true believer must confess his sins, all of them, once a year to the priest, and they affixed to it this declaration, that there is no hope of pardon …
Charles Haddon Spurgeon—Spurgeon's Sermons Volume 3: 1857

Letter xxii. St. Ambrose in a Letter to his Sister Gives an Account of the Finding Of...
St. Ambrose in a letter to his sister gives an account of the finding of the bodies of SS. Gervasius and Protasius, and of his addresses to the people on that occasion. Preaching from Psalm xix., he allegorically expounded the "heavens" to represent the martyrs and apostles, and the "day" he takes to be their confession. They were humbled by God, and then raised again. He then gives an account of the state in which their bodies were found, and of their translation to the basilica. In another address …
St. Ambrose—Works and Letters of St. Ambrose

The Progress of the Gospel
Their sound went into all the earth, and their words unto the end of the world. T he heavens declare the glory of God (Psalm 19:1) . The grandeur of the arch over our heads, the number and lustre of the stars, the beauty of the light, the splendour of the sun, the regular succession of day and night, and of the seasons of the year, are such proofs of infinite wisdom and power, that the Scripture attributes to them a voice, a universal language, intelligible to all mankind, accommodated to every capacity. …
John Newton—Messiah Vol. 2