Psalm 15 starts by asking: "Who may abide in God's Presence", enjoying His hospitality, provision, protection & fellowship (v1), and then gives 10 descriptions of the character of those able to dwell with God (v2-5a), followed by a concluding promise of blessing for those who do abide in Him (v5b). It describes how to abide in FELLOWSHIP with God; not a prescription for salvation, which is not based on our righteousness, but Christ's. (Ps 24:3-10 deals with salvation). The mention of God's Tabernacle in v1 points to the picture of the Tabernacle of Moses, which reveals that our access into God's Presence is only by the Blood of Christ.
In Christ, we can now enjoy fellowship with God, by abiding in His Presence and partaking of His blessings. However, fellowship is not automatic. By its very nature, it requires the co-operation and participation of both parties. Fellowship is based on reciprocation, giving & receiving. Whereas salvation is binary, fellowship differs by degrees. The more their hearts & lives harmonise and the more each is willing to give to the other, the deeper their fellowship becomes. God invites us into fellowship, but the degree to which we abide in His Presence depends on us. The more we turn to Christ and draw near to Him, the more of His Spirit, glory & light we will receive, transforming us into His image from glory to glory, and the more our heart is united to him, in harmony with Him, the closer we can be to Him, and the greater fellowship we'll enjoy with Him. He has opened His heart to us, and it's now up to us how much we enter into His Presence - we determine how close we are to God. What hinders us? To draw near to God in fellowship requires that our we harmonise our heart & life to Him, in submission to and agreement with His will, which includes obedience (Amos 3:3). Thus, we must be willing to repent, change & align our lives with His ways, which is contrary to our flesh, so we must die to self (our independent soul-life).
Thus v2-5 describe 10 aspects of the righteousness & nature of Christ, of which we partake when we are saved. The more we abide in Him, the more these qualities are manifested in our lifestyle. Thus they are the characteristics of those who are in harmony with God, walking in fellowship with Him. Also, the more we embrace these aspects of righteousness into our character & lifestyle, the more we harmonise with God, so our walk with God becomes closer. Our fellowship with God depends on our heart condition, which depends on our obedience in our life. When we act contrary to God's righteousness, we harden our heart, so our fellowship decreases, but when we obey God, our heart becomes softer (more submissive) to God, bringing us into more intimate fellowship (John 15:1-14). Thus these 10 points shows us areas, where we can increase our obedience to God, so we can abide in Him more deeply. The 1st characteristic: "He who walks uprightly" (v2a) speaks of being devoted wholly to the Lord. All the other 9 speak of how we are to express this devotion in the way we treat others, made in His image (see 1Jn 2:9-11, John 15:9-14, Mark 11:25, which teach our fellowship with God is conditional on whether we walk in love towards people). The 2nd & 3rd characteristics summarise our righteous lifestyle before men, doing what is right and speaking the truth from the heart (v2b). These are then developed in more detail. The 4th, 5th & 6th are negatives, which the righteous man refuses to do: (4) back-bite, gossip and slander others, (5) he does no harm to his neighbor, and (6) his ears are not open to gossip, he does not believe the worst of people without basis or evidence, and is not quick to take up an offence against someone (v3). (7) He is discriminating and disapproves of those given over to evil. He hates sin (Prov 8:13), but honors those to love God, and (8) he is faithful to his word, keeping his promises & commitments even when it costs (v4). He's not a greedy money-lover, but is honest and generous with his finances. He handles his money with integrity. (9) He does not charge excessive interest, which is usury (v5a). Interest can be charged to foreigners and as part of normal business transactions (Deut 23:19,20; Matt 25:27), but not to a fellow brother (Israelite) who has fallen on hard times, thus adding to his hardship. It's wrong to profit from the poor and helpless. In such cases they were not to charge any interest (Lev 25:35-38, Ex 22:25, Neh 5). (10) He does not use bribery to corrupt the judicial process (v5b, Ex 23:6-8, Deut 16:18-20, 27:25). He doesn't treat people as more important than things.
Psalm 15 concludes with the promised blessing of the man who practices these things and so abides in God's Presence - He'll never be moved or shaken (v5b). Through dwelling in God's Presence, he is filled with His peace and strength, giving him stability (Psalm 1).