- The Letter of Athanasius, Our Holy Father, Archbishop of Alexandria, to Marcellinus on the Interpretation of the Psalms. 300-373 AD, 45 years a bishop, 5 exiles, defender of Trinity against Arianism. Owe the preservation of the Faith in large part to his heroic sufferings. Church Father.
“It is possible for us therefore, to find in the Psalter not only the reflection of our own soul’s state, together with precept and example for all possible conditions, but also a fit form of words wherewith to please the Lord on each of life’s occasions, words both of repentance and of thankfulness, so that we fall not into sin; for it is not for our actions only that we must give account before the judge, but also for our every idle word.” 
Let no unwholesome talk come from your mouth. Eph 4:29
Psalms are a special treasure summary of the Faith applied to the individual person; one could call the psalms a summary of all scriptures.
- Structure of Psalter into five books: I Ps 1-41, II 42-72, III Ps 73-89, IV Ps 90-106, Ps V Ps 107-150. Each book of the psalter tends to have a particular tone.
Following the indications of Athanasius consider Ps 15, Book I, tone is part of the Laments of David.
Lamentation= A song of sadness for misfortune, or a dirge for the dead. One-third of the Psalms are lamentations, and other similar lamentations are scattered throughout the OT.
- Psalm 15 Citizen of Heaven founded on actions of Citizen of Earth, grace builds on nature
Short 5 verses, David author, circa 979 BC, audience all those who want to live in heaven
- Jesus is the New David, the real David as the early Church quickly testified to. Thus, as David is the author of Psalms, now Jesus can be seen through Our Lord’s eyes. This is a concrete example of the New hidden in the Old, and the Old made manifest in the New. Ratzinger succinctly summarizes this very point.
“Psalms recited in a new way without discontinuity- as a prayer in communion with Jesus Christ. Augustine offered a perfect explanation of this Christian way of praying the Psalms- a way the evolved very early on- when he said: it is always Christ who is speaking in the Psalms- now as the head, now as the body (for example Ps 60:1-2: 61:4; 85:1,5) Yet through him- through Jesus Christ- all of us form a single subject, and so in union with him, we can truly speak to God.”
Who Shall Abide in God’s Sanctuary?
A Psalm of David.
15 O Lord, who shall sojourn in thy tent (temple, heaven)?
Who shall dwell on thy holy hill? (repetition synonymous, Hebrew poetry)
2 He who walks blamelessly, and does what is right, (practical advice, hokhmah)
and speaks truth from his heart;
3 who does not slander with his tongue,
and does no evil to his friend,
nor takes up a reproach against his neighbor; (repetition)
4 in whose eyes a reprobate is despised, (truth)
but who honors those who fear the Lord; (worth the sacrifice)
who swears to his own hurt and does not change; * (pay day loans, credit cards)
5 who does not put out his money at interest,
and does not take a bribe against the innocent.
He who does these things shall never be moved. (moved from where? verse 1 tent)
*Speaking truth is what a righteous man does, he does not converse with reprobates, liars, and will honor his word, keep promises, even at the cost to himself, his own hurt
Sojourn, pilgrims, this life is not home but for dwelling with the Lord, do no evil, practical rooted in love
 Scott Hahn, Catholic Bible Dictionary (Doubleday Religion: NY 2009) 523
 Joseph Ratzinger, Jesus of Nazareth Part Two Holy Week: From the Entrance Into Jerusalem to the Resurrection (Ignatius: San Francisco 2011) 146