How can young people keep their way pure? By guarding it according to your word. (v9)

Those in good soil are the ones who, when they hear the word, hold it fast in an honest and good heart, and bear fruit through patient endurance. (Luke 8.15)

With my whole heart I seek thee; let me not wander from thy commandments! (v10)

When the soul has become enraptured by the beauty of the Word, captivated by His unfolding light in the mind, it ever seeks greater union with Him.  It is left with only one fear: knowledge of its past and its own weakness brings fear that it will wander from the path of love once again.  Therefore there is only one thing to do: beseech God to take from it the most precious gift to it - free will.  As long as there is free will there is the possibility of straying on this earth.

It is possible to relinquish one's free will.  Only through obedience can one deny one's own will and bind it to God's will. Christ accomplished this perfectly.  "I came not to do my own will but the will of Him who sent me."  Christ, as a separate person of the Trinity, has his own will.  But he subjects it perfectly to the Father's will.  Why?  Love.  Though Christ's will is perfect in itself, and is the subject of our desire, he shows us how to attain unity with himself by showing us how he is united to the Father.  Mystery of mysteries!  Our path to union with Christ is the same path Christ took to the Father while on earth.  He draws us to this by the Holy Spirit.  If the path is the same will not the result be the same?  Perfect union with Christ.  "I in them and you in me, that they may become completely one." (John 17.23)

I have laid up thy word in my heart, that I might not sin against thee. (v11)

Can this not be seen as a foreshadowing of the way in which Christ interiorized the external law?  "The law tells you not to commit adultery.  I tell you whoever looks lustfully at a woman has already committed adultery in his heart.  The law tells you 'thou shall not kill' but I tell you whoever grows angry with his brother in his heart shall be liable to judgment."  The law brought the moral code.  The prophets pointed the way to Christ, who is the perfection of the Law.  This prophetic psalm foretells how the external law will be transformed into an indwelling abode of Christ in the heart.  He wants nothing bad in his dwelling; we want to meditate on the Word (him) to ensure this doesn't happen.

In the way of thy testimonies I delight as much as in all riches. (v14)

Who has found the place of wisdom, who has penetrated her treasuries? (Baruch 3)

Open my eyes, that I may behold wondrous things out of thy law. (v18)

Then he opened their minds to understand the scriptures. (Luke 24.45)

My soul is consumed with longing for your ordinances at all times. You rebuke the insolent, accursed ones, who wander from your commandments. (v20)

Only pride drives away Jesus from a soul.  Humility draws him like perfume.  "Take my yolk upon you, for my yolk is easy, and my burden light." (Matthew 11.29)

Even though princes sit plotting against me, your servant will meditate on your statutes. (v23)

The princes of darkness do plot and lie in wait for those who set forth in good will to meditate more deeply on the Word. Laziness, boredom, fatigue, excessive concern for one's time, the despair of learning the truth and so on are all temptations awaiting one, to test one's resolve.

My soul clings to the dust, revive me according to your word. My soul melts away for sorrow; strengthen me according to your word. (v25,28)

The soul humbles itself and recognizes its unworthiness before God.  It recognizes it has clung to earthly ways and, sorrowful, it longs to be recreated according to the Word.

I cling to your decrees, I run the way of your commandments. (v31,32)

And now the soul not only follows the law, but runs in the way of the word.  How?  "For you enlarge my understanding." (v32)  This is as it is written: "bow humbly under God's mighty hand so in due time he may raise you up." (1 Peter 5.6)  And again, "choose the lowest place at the banquet so the master may invite you up higher." (Luke 14.10)

v33-40:
"Teach me, give me understanding, lead me, turn my heart, turn my eyes from vanities, confirm to your servant, turn away the disgrace I dread."  Listen to the humility of a soul which longs to be united to God's ways instead of its own.  It recognizes the profound mystery behind the letter of the law, which can easily be read and understood from the human perspective, by begging for understanding. It recognizes its own willfulness and tendency toward worldly gain by praying "turn my heart to your law and not to selfish gain" ("lead us, not into temptation").  It knows the dangers of dissipation and its own weakness when it prays "turn my eyes from vanities."  Finally, it acknowledges its many past failures when it prays to be delivered from its former way of sin, that is, "the disgrace I dread."  All of this yearning is ultimately for Christ, who is the complete fulfillment of the Law, Wisdom Incarnate, who alone can fully satisfy such deep longing for righteousness.

Contrast this with the soul which has been shaped by the perversions of modernity.  It does not believe it needs taught by God.  It believes it possesses sufficient understanding of his commandments.  It does not want led.  It's heart is absolutely set on selfish gain.  And it does not dread sin but rather seeks it as liberation and proof of it's free-will.

"Take my yoke upon you, and learn from me; for I am gentle and humble in heart, and you will find rest for your souls. For my yoke is easy, and my burden light." (Matthew 11.29-30)