Your reading of this passage is very close to my own, and since you blend both the communal Jubilee Year with the personal aspect of forgiveness, I am free to focus on other matters.
First let me offer some comfort to those who may be troubled about the different versions of this teaching in Matthew and Luke. In Matthew Jesus speaks of “debts” while in Luke he speaks of “sin.” Both may be correct. The Gospels are written in Greek but Jesus most likely preached in Aramaic, the vernacular of his listeners. In Aramaic the word “choba” means both debt and sin, and it is this word Jesus spoke and which Matthew and Luke both translated rightly even as they translated differently.
Second and more importantly, I am struck (and if I were a Christian troubled) by Jesus’ teaching on forgiveness. Jesus says nothing about praying in his name or believing in him as the Son of God as a condition for forgiveness. Rather it links the forgiving of others to God’s forgiving of us. This is very much in line with Jewish thinking then and now.
In the second century BCE text the Wisdom of Ben Sirach we are instructed, “Forgive your neighbor the wrong he has done, and then your sins will be pardoned when you pray” (Ben Sirach 28:2, NRSV). In the Talmud God says, “I forgive your sins against Me, but go to those against whom you have sinned and ask their pardon also” (Rosh HaShanah 17b). In the older text God’s forgiveness requires us to get the forgiveness of others. In the later text God’s forgiveness comes before human pardon and is an impetus for it.
Jesus differs from Sirach and the Talmud by focusing on giving forgiveness to others rather than asking us to forgive us though this too can be found in rabbinic teaching, “All those who are forbearing and forgiving of others and who do not insist on their rights will be forgiven their sins” (Talmud, Yoma 23a). This last text may be the source of Jesus’ teaching in Mark, “Whenever you stand praying, forgive, if you have anything against anyone; so that your Father in heaven may also forgive you your trespasses” (Mark 11:25).
In all these cases, however, it is clear that belief in Jesus has nothing to do with securing God’s forgiveness. Forgiveness is ours to bestow, and when we do so God does likewise unto us. This a variation on the Golden Rule: Do unto others as you would have God do unto you.”
I am neither a theologian nor a scholar of Christian history, so I am wondering why and when Christianity shifts from the Jewish teaching of Jesus about forgiveness to the Christian teaching of forgiveness through Jesus? Not that you need more work to do, Mike, but I look forward to hearing your answer and insight into this.