There is nothing unusual in the question that Jesus is asked in our Gospel today (Matthew 22:34-40) - students would regularly ask visiting Rabbis this question - which is the greatest commandment. When there are 613 mitzva (commandments) to choose from in the books of Moses (the Torah or Pentateuch) it is no wonder that various people had attempted to rank and order them to make them more useful. So we see, for example, in Luke 10, that Jesus poses the question back to another lawyer who asks him what he must do to receive eternal life (which leads into the parable of the Good Samaritan) and we have a range of alternative answers available in the Rabbinic writings that support the choices of Jesus or offer alternatives.
The first commandment that Jesus calls upon is the most logical choice of any devout Jew who was called upon to recite the Shema at least twice daily - 'Hear O Israel, the Lord is God, the Lord is one' (Deut 6:4) which leads into the prescriptive commandment (rather than the proscriptive commandments like 'you shall not steal' or 'you shall not kill' - which comprised 365 of the laws - one for each day of the solar year; leaving 248 prescriptive commandments like 'honour your father and mother' - one for each of the organs in the human body) to 'love the Lord your God with all your heart, mind and soul'. For the second commandment, Jesus jumps two books earlier to Leviticus, quoting from the end of Lev 19:18 to provide the missionary outcome of the first commandment - 'to love your neighbour as yourself'.
The first commandment then provides the basis of the first reason that the Church exists - to gather for worship and adoration of God as our expression of our love. The second commandment then addresses our need to share that love in works of compassion and evangelisation.
Recorded at St Paul's, 6pm Vigil (10'30" - including final blessing)
Sunday 30, Year A.