Debtors vs. Trespassers I converted to the Presbyterian faith from a Catholic upbringing a while back and have always wondered - but never had anyone to ask - why Catholics use "Trespassers" in the Lord's prayer (Please forgive our trespasses, as we forgive our Trespassers) and the Presbyterians use "Debtors".  I'm sure someone has to have asked this question somewhere before me :-)
There's a great analysis by Dave Armstrong that goes into a lot more detail, but it comes from trying to best capture the point of the Lord's Prayer—as it's rendered in the Bible—in English.

There are two forms of the Lord's Prayer found in the Bible: one in Matthew and another in Luke.

In Matthew 6:9–13, the Lord's Prayer is rendered as (emphasis mine):


  9“This is how you are to pray:  
  
  Our Father in heaven,
  hallowed be your name,
  10your kingdom come,
  your will be done,
  on earth as in heaven.
  11Give us today our daily bread;
  12and forgive us our debts,
  as we forgive our debtors;
  13and do not subject us to the final test,
  but deliver us from the evil one.


But in Luke 11:2–4, it's rendered as (emphasis mine):


  2He said to them, “When you pray, say:
  
  Father, hallowed be your name,
  your kingdom come.
  3Give us each day our daily bread
  4and forgive us our sins
  for we ourselves forgive everyone in debt to us,
  and do not subject us to the final test.”


Given it's more fleshed out, most Christians favor Matthew's version. In the original Greek, the word used in Matthew 6:12 is ὀφειλήματα, which means "debts". The word used in Luke 11:4 is ἁμαρτίας, which means "sins".

So, to be in line with the original manuscript, "debts" is the correct word, and indeed, most Christians (including all non-English Catholics) use "debts".

In English, however, "debts" and "debtors" usually refer to a loan: a monetary debt to a bank, for example. But later on in Matthew, it says:


  14If you forgive others their transgressions1, your heavenly Father will forgive you
  15But if you do not forgive others, neither will your Father forgive your transgressions1.


So while the actual word is "debts", it's clear the point of the Lord's Prayer is to say that one ought to forgive those who wrong us, just as God forgives us our sins and transgressions, not that we ought to forgive loans made upon us (i.e., God doesn't "loan" us sins).

To make clear the point of the prayer,"debts" was replaced with "trespasses". This translation became popular in 16th century England, even making it into the Book of Common Prayer. The Roman Catholic version of the Lord's Prayer is almost identical to the Book of Common Prayer's version at the time, and has not been changed since then.

Interestingly, the English version of the Missal recently underwent a fairly dramatic change as things were retranslated to better correspond to the original meaning of words, but the Lord's Prayer was skipped. I could not find any explicit justification for the omission, which suggests to me that the Vatican still considers the use of "trespasses" to accurately convey the intent of the prayer.



Note 1: Also translated as trespasses, depending on the translation.