But every Lord's day gather yourselves together, and break bread, and give thanksgiving after having confessed your transgressions, that your sacrifice may be pure. But let no one who is at odds with his fellow come together with you, until they be reconciled, that your sacrifice may not be profaned. For this is that which was spoken by the Lord: "In every place and time offer to me a pure sacrifice; for I am a great King, says the Lord, and my name is wonderful among the nations."
Here the writer talks about our sacrfice being pure. That is very intertesting. According to most Protestants, there are no more sacrifices, and yet here this author wrote about confessing our sins so that our "sacrifice may be pure" and to reconcile ourselves to others that our "sacrifice may not be profaned".
Also in the context, there can be a good argument that this "sacrifice" is the Eucharist.
First of all, the author is talking about the "breaking of the bread", which is a term used by early Christians for the partaking of the Lord's supper.
Second, the author quotes from Malachi 1:11. Here is the exact verse:
For from the rising of the sun even to its setting, My name will be great among the nations, and in every place incense is going to be offered to My name, and a grain offering that is pure; for My name will be great among the nations," says the LORD of hosts.
Here the Lord predicts that there will be a time when the Gentiles (nations - Goyim) will be offering a pure offering (sacfrice) to God. This sacrifice will not be a sacrifice of animals, but of bread (grain offering). This prophesy could not have possible been fullfilled under the Old Testament. Under Old Testament, sacrifices can only be offered by Jews in the Temple. So this fullfillment can only be by the Gentile Catholics throughout the world when they offered the Eucharist to God in union with Christ's one-time sacrifice on the cross. Only by there being a sacrificial aspect to the Lord's Supper could this be fullfilled.
Justin Martyr (about AD 150) also quoted this passage in Malachi and linked this sacrifice being offered by Gentiles throughout the world as Christians offering the Eucharist to God.
This shows that the earliest non-Biblical evidence points to the Catholic teaching on the Eucharist.