Here's an interesting and little-known fact about Luther's translation of 2 Corinthians 5:19.
If you look up 2 Corinthians 5:19 in an online version of what is supposedly Luther's German Bible of 1545, it reads,
Literally, this reads, "For God was in Christ and reconciled the world with himself and did not reckon their sins to them and has established among us the word about the reconciliation (- or, "the word of reconciliation")."
Some have pointed this out to demonstrate that Luther clearly saw a one-time, past tense justification of the whole world. "Reconciled the world..." "Did not reckon..."
However, students of translation history recognize that the text of this supposed 1545 Bible is corrupted in places and not always an exact replication of Luther's actual 1545 Bible. One can download digitally photographed copies of Luther's original Bibles (here's one example from 1530), or there's a handy website entitled http://lutherbibel.net/ that has reproduced the exact text in an easily searchable format. This is called the Ausgabe letzter Hand.
In the Greek, 2 Corinthians 5:19 has one imperfect main verb (God "was"), and then two present active participles ("reconciling," "reckoning"). Instead of turning these into past tense indicative verbs as the corrupt versions of Luther's Bible have it, here is Luther's original wording of 2 Corinthians 5:19 (the same in 1545 as it was in 1530):
Luther used present tense verbs, not past tense verbs. Literally, "For God was in Christ, and reconciles the world with himself, and does not reckon their sins to them, and has established among us the word about the reconciliation."
When Luther wanted to use a third person singular past tense of "to reckon," as in Genesis 15:6, he used the word "rechent." But the fact that he uses a present tense verb in 2 Corinthians 5:19 ("rechnet") is further evidence that he viewed the present tense Greek participle, not as referring back to a one-time event that took place on the cross, but to the ongoing reconciling of the world that God accomplishes through the ministry of the Word, which proclaims a God who gave His Son for the world as the price of reconciliation and as the perpetual Reconciler between God and sinners, who reconciles sinners to God, not "whether they believe in Him or not," but through faith.
In other words, Paul is teaching nothing in 2 Corinthians 5:19 but the very same thing that Jesus taught as recorded in John 3:16-18. God loved the world. God gave His Son as a sacrifice to reconcile the world to Himself. All who believe in the Son are reconciled with God. Those who don't believe in Him remain in condemnation.