Psalm 16 is an important Messianic Psalm, quoted by Peter & Paul to prove Jesus is the promised Messiah. Peter quoted Ps16:8-11 in Acts 2:25-28 and expounded it in Acts 2:22-33, as a central part of his sermon. It speaks of a Man who dies and His soul goes to Sheol, but is resurrected before His body sees corruption (within 3 days). Also, He is then exalted to God's right hand (v9-11). He points out the Psalmist, David, died and is still in his tomb (his body saw corruption). Thus, it was not fulfilled by David, but rather he spoke by the Spirit of Prophecy about Christ, the Son of David, that He'd be resurrected before his body saw corruption (v29-31). He then said Jesus fulfilled this Prophecy by His 3rd day resurrection, proving He is the Christ (v32,36). He also pointed out Jesus was exalted to God's right hand, fulfilling Ps 16:11 & 110:1, as confirmed by the Outpouring of the Spirit (Acts 2:33-35). Likewise, Paul in Acts 13:35 quoted Ps 16:10 and expounded it in Acts 13:36-39 to prove Jesus is the Christ. Thus though we can read much of Ps 16 as David's words of trust in God for preservation & provision in this life and hope for his eternal life in God's Presence, the words only find ultimate fulfilment in Christ. So, we should read them as Christ's words, given by prophecy, as He approached death, expressing His faith in God to resurrect Him. Although God, He had to live as a man totally depending on God for everything, including His resurrection: "Preserve me, O God, for in You I put my trust...You are my Lord, My goodness is nothing apart from You (or 'every good thing comes from You')” (v1-2). He's our perfect example of how to live by faith. He describes the saints (those who trust in Him) as the excellent (noble) ones, in whom is all His delight (v3). This shows Christ had us on His heart & mind as He went to the Cross. We are precious in His sight, and so gave Himself for us, so we might be His forever: "for the joy (us, His Bride) set before Him, He endured the Cross" (Hebrews 12:2).
As our example, He reveals a key part of living by faith - the rejection of all other gods & idolatry (v4), including covetousness (Col 3:5), for men turn from a pure devotion to the true God and hasten after (seek) other gods is to possess what they offer (prosperity). But the more they multiply their gods & idols the more their sorrows multiply (v4). A classic example is Man's Fall. God provided abundantly, and would have given them more, as they proved themselves faithful, but listening to Satan made them dissatisfied with His Presence and their allotted inheritance, so they became covetous to gain more, and so rejected His authority, claiming autonomy as their own gods, and went their own way, but soon found they gained nothing, but rather lost His Blessing, and their sorrows multiplied. The truth is if we seek 1st the Kingdom (reign) of God over our life and live by His righteous Spirit in our heart, all things will be added to us (Matt 6:33). Thus, we need to learn to be satisfied (content) with God Himself (His Presence in our heart), and with whatever inheritance of possessions & experiences He chooses to give us (as a bonus), both now, in the future and in eternity (Rev 21:7, Phil 4:11-13, 1Tim 6:6). This is exactly what David & Christ declare: "O Lord, YOU are the PORTION of my INHERITANCE and my CUP (what God appoints for me to experience); You maintain my LOT (if we trust Him, He will guard our eternal inheritance, so none can steal it). The (boundary) lines have fallen to me in pleasant places. Yes, I have a GOOD INHERITANCE" (v5-6). God is generous (good), giving us much more than we deserve, so we can submit to Him and trust Him day by day for His Presence & gracious provisions, rather than turning from Him in striving & lust to grasp what He's not giving us at this time. In this manner, He declares: "I have set the Lord (not things or experiences) always before Me... I shall not be moved" (v8). As a result, He has assurance God will guide & preserve Him by His Presence on the path of life, thru this life, then thru death & resurrection and exaltation to God's right hand in Heaven, where He'll give Him fullness of joy in His Presence & pleasures (experiences) for all eternity: "You will show me the path of life. In Your Presence is fullness of joy; at Your right hand are pleasures forevermore" (v11). These verses also apply to us, for we are "heirs of God & joint heirs with Christ" (Rom 8:17). He's our example to follow, that we should trust in God and be satisfied with His Presence in our hearts, and the possessions, gifts, opportunities, positions, blessings & experiences He gives us in this life, knowing He’s prepared a wonderful eternal future and inheritance for us, way beyond our present experience & imagination (1Cor 2:9, Eph 2:7), where we'll be exalted and experience fullness of joy in His Presence.