The original collect is from the Sacramentary attributed to Leo I (pope 460-461), a fragmentary collection of prayers.) [1]

      Psalm 1 is appointed for use four times in the three years of the lectionary, twice in year C and once each in years A and B. It is a wisdom meditation on the contrasting paths of the wicked and the righteous. As a response to the first lesson, it exemplifies the holiness of Israel.

1. Happy are those…: The Revised Standard Version has "Blessed is the man…" (the noun is singular). The form is the beatitude, like those in Matthew 5:3 ff or Luke 6:20 ff.
wicked…sinners…scoffers: The periphrastic translation of New Revised Standard Version loses the sequence "walks…stands…sits" for the three representatives of the ungodly. "…the psalmist shows in detail and in phrases which are progressively intensified the various possible ways that lead to sin, and he does so by using concrete examples. The least sinful way is dealt with first, namely the way of ‘walking in the counsel of the wicked’, which means letting oneself be guided by the advice of evildoers. Then there is the ‘standing in the way of sinners’, which means conforming to the example of sinners. And finally, the worst sin is that of taking a seat in the meetings of the scoffers and actively participating in their mocking of the things which are sacred." [5]
2. their delight: The pronoun is singular as are the other pronouns in the Psalm. The one who delights in the law of the Lord has a secure and fruitful life (verse 3).
the law of the Lord: Torah "is ‘instruction’ in the sense of the ‘merciful revelation of the will of God’ (cf. G. von Rad OT Theol, 1:190ff.)." [6]
4-5. The wicked are…like chaff: The wicked are without substance or vigor; they will not survive the judgment.
6. the way of the righteous…of the wicked: It is God who determines which way will endure and which will disappear.

2. we had already suffered and been shamefully mistreated at Philippi: Paul and Silas had been arrested and illegally beaten in Philippi, the first city to the east on the Egnatian Way from Thessalonica (Acts 16).
great opposition: Paul and Silas had taught in the synagogue for three weeks. Some Jews and many Gentiles who worshipped in the synagogue became believers. There was violent opposition from the Jews; Jason, their host, had to furnish a peace bond, and Paul and his colleagues went to Beroea (Acts 16:19-24, 35-40).
3-7: Paul’s description of the motivations for his ministry in Thessalonica no doubt mirrors the accusations that were advanced against him. His motives were not pure. He was a trickster. He taught an attenuated religion that did not require any effort. He was always looking for approval and making demands. In response Paul says he is not motivated by "deceit or impure motives or trickery," but by a desire to please God.
8. we are determined to share with you…our own selves, because you have become very dear to us: Paul expresses his deep feelings for the Christian community in Thessalonica. Paul and his colleagues are the examples of the love of neighbor which is an expression of the meaning of the law both in Leviticus and Matthew. Such love does not arise out of base motives, and it is not hindered by violence. Instead it is an expression of the love God has for his people. [10]

     In the Talmud there are four kinds of questions: The first type of question is the halakhic question, concerning the law; the second, questions of haggada, questions about apparent contradictions between different verses from Scripture; third, questions of boruth, third are mocking questions which ridicule the belief of the rabbi, and fourth, questions about the principles of morality.
     In the Passover service four questions are asked by the youngest son. Traditionally there are also four types sons, the wise son, the wicked son, the pious son and the son who does not know how to ask.
     The section Matthew 22:15-46, which includes four questions are "representative of four different types of question distinguished by the early Rabbis." [7] The questions concern whether tribute to Caesar was lawful (Matthew 22:15-22), halakha); whose wife the woman married to seven brothers would be (Matthew 23-33, boruth); which is the greatest commandment in the law (Matthew 22:34-40, principles of morality; and why David called the Messiah, Lord (implying "Yahweh") if the Messiah is David’s son (Matthew 22:41-46, haggada). [8] It is likely that the structure of this passage is reflects these two traditional structures, with a Pharisee asking a question of law, the Sadducees asking question mocking the doctrine of the resurrection, the lawyer asking about the greatest question, and Jesus asking a question of haggadha, a contradiction in Scripture on behalf of the one who does not know how to ask.
34. he had silenced the Sadducees: The Sadducees had sought to reduce the doctrine of the resurrection to an absurdity, but Jesus astounded the crowds by showing that God was not a God of the dead but of the living.
35: In Mark the question is asked by a scribe. A Pharisee who was a lawyer asked Jesus to identify the greatest commandment in the Torah. Jesus replied that it was the instruction that accompanied the Shema’ (Deuteronomy 6:4-5). Nomikos, "lawyer," is used in Matthew only here. Otherwise, in the New Testament it is used only by Luke, "who often uses it as the equivalent of  "[grammateus]," ‘scribe.’" [9]
37. And he said to him: In Matthew and Mark Jesus answered the Pharisee. In Luke Jesus turns the question back to the lawyer and he answered.
You shall love the Lord your God: In Mark 12:29 Jesus quotes the beginning of the Shema’ from Deuteronomy 6:4, and then continues with 6:5. Matthew omits the beginning of the Shema’.
with all your heart, and with all your soul, and with all your mind: In Hebrew the heart is the organ of thought, so the addition of "with all your mind" at the end of the quotation is an annotation which provided the Greek reader with an interpretation of the word "heart."
39. You shall love your neighbor as yourself: Leviticus 19:18: Jesus adds the second law, which elsewhere in the New Testament is identified as the summary of the Law: see Galatians 5:14: "the whole law is summed up in a single commandment, ‘You shall love your neighbor....’" Romans 13:9: "The commandments...are summed up in this word, "Love your neighbor...." James 2:8: "the royal law according to the scripture, "You shall love your neighbor...." 1 John 4:20-21: "Those who say, ‘I love God,’ and hate their brothers or sisters, are liars; for those who do not love a brother or sister whom they have seen, cannot love God whom they have not seen. The commandment we have from him is this: those who love God must love their brothers and sisters also." In Leviticus the neighbor is a fellow Israelite, and the reason for the admonition to love is that both one’s neighbor and one’s self belong to Yahweh. Loving one’s neighbor is grounded in one’s love for Yahweh.
40. On these two commandments hang all the law and the prophets: The law and the prophets is the first century way to say "The Old Testament." Paul makes the same assertion in slightly different form: ‘Owe no one anything, except to love one another; for the one who loves another has fulfilled the law. The commandments, "You shall not commit adultery; You shall not murder; You shall not steal; You shall not covet"; and any other commandment, are summed up in this word, "Love your neighbor as yourself."’
41-46: Having disposed of the Pharisee’s test Jesus offers a challenge of his own: Who is the Messiah? Daube sees this as a reflection of the description of the four kinds of sons who ask questions during the Passover Seder. The last son is the one who does not know how to ask, and for whom the father must ask the question. [10] The question that Jesus asks is of the character of haggadha, a question about a seeming contradiction in scripture.
42. The son of David: This is a correct answer. The Messiah was an anointed prince of Israel, a descendant of the dynasty of David. In Matthew Jesus is frequently identified as the "Son of David" (Matthew 1:1 and throughout). Now Jesus springs his trap.
43-45. How is it that David by the Spirit calls him Lord, saying, ‘The Lord said to my Lord, "Sit at my right hand until I put your enemies under your feet."’?: The form of the question depends on the Greek form of the Psalm since in the Hebrew the first "Lord" is the name Yahweh. The meaning of the Psalm verse in Hebrew is: "Yahweh said to my Lord (David)…." Jesus in Matthew’s Gospel interprets the Greek form of the Psalm to say that David (the Lord) said to the Messiah (my Lord). So, the Messiah "must be greater than David, because David calls him Lord." [11]
46: Daube suggests that this statement should be introductory to verse 45 and indicates the quandary of the son who does not know how to ask, so the father must pose a question for him. [12] Others see this as Jesus total victory over his questioners.