My teacher just told us that the verse in Luke where Jesus sweats blood was not in the original text and is a textual issue. Have you heard this argument before?
It is true that Luke 22:43-44 is not included in the majority of the oldest and most reliable manuscripts of Luke. This passage is among the group of about six passages in the entire New Testament which are in dispute. In all six cases, it appears that early scribes added a small comment which was later included into manuscripts. The entire list of such significant “interpolations” is this: Luke 22:43-44, John 8:1-11, 1 John 5:7-8, Mark 16:9-20, Acts 8:37 and John 5:4. This amounts to less than one half of one percent of the New Testament. In the case of John 8:1-11, it is the consensus of scholars, both ancient and modern, that this is part of the original Christian tradition and represents a genuine event in the ministry of Jesus. The question is not whether this scene is genuine, but whether it was originally in John in what we call chapter 8. The same is likely true of Luke 22:43-44, as I will mention below. In the case of 1 John 5:7-8, Acts 8:37 and John 5:4, these three appear to have been added later in order to support orthodox teaching against heresies, but are certainly additions and have no early support, so they can be rejected as simply not belonging in the New Testament at all. The case of Mark 16:9-20 is the only one over which there is really any significant debate as to whether it is genuine or not. This case is complicated and I will not discuss it here.
Here is the list of those that do or do not include Luke 22:43-44:
Codex Sinaiticus*, 2, D, Codex Laudianus, Codex Seidelianus I, Codex Seidelianus II, Cyprius, Regius, Codex Campianus, Guelferbytanus B, Codex Sinopensis, Codex Nanianus, Codex Monacensis, Δ*, Codex Tischendorfianus III, Codex Athous Lavrensis, Uncial 0171, f1, 174, 565, 700, 892, 1009, 1010, 1071mg, 1230, 1241, 1242, 1253, 1344, 1365, 1546, 1646, 2148, 2174, (ℓ 184, ℓ 211, Byz, it, vg, syrcur, syrh, syrp, syrpal, Armenian and Ethiopian manuscripts, Diatessaron.
Papyrus 69, Papyrus 75, Codex Sinaiticus1, Codex Alexandrinus, Codex Vaticanus, Codex Petropolitanus Purpureus, Codex Nitriensis, Codex Borgianus, W, 158, 512, 542, 552, 579, 777, 826, 1071*, 1128, Lectionariespt, f, syrs, copsa, copbo, Georgian mss.
You can see that most Greek manuscripts of the New Testament include Luke 22:43-44, but the earliest and those generally considered most authoritative (the papyri, Alexandrinus, Vaticanus and Sinaiticus) do not. By the way, it is possible that Luke 22:43-44 was in the original. In fact, Church fathers such as Hippolytus, Justin Martyr and Irenaeus–all from the second century–quote this passage, and these quotes are older than any of the manuscripts above. It is perhaps as likely that someone later removed the passage as too difficult to accept as it is that someone included it on order to support the humanity of Jesus. I would say it is perhaps 50:50. My conclusion, based on the writings of Irenaeus, Justin and Hippolytus is that this is a genuine story from the accepted oral tradition about Jesus. I believe that it almost certainly actually happened, but that it may or may not have been in the original Luke. In other words, like John 8:1-11, I would not hesitate to use it in a sermon, but would be cautious in basing an essential teaching of Christianity on these passages. In fact, no essential teaching of Christianity rises or falls on John 8:1-11 or Luke 22:43-44.
By the way, I definitely would NOT use 1 John 5:7-8, Acts 8:37 or John 5:4 in any teaching or preaching.
So, your professor may slightly exaggerate the negative case for Luke 22:43-44 when he simply declares it not in the original. But his comment, even if overstated, is appropriate. The fact is that the New Testament was passed on by scribes and that a number of extremely minor issues were created by copying errors, most of which are very easily corrected. However, there is also a much smaller number of significant issues were created by scribes, but virtually the entire list of such texts is mentioned above. None of these disputed texts do anything at all to the essential facts or teaching about Jesus of Nazareth. The reason we have these disputes is that we have literally thousands of Greek manuscripts. The information is so large, including the quotes of early Christian writers, that we can, with confidence, produce a Greek New Testament which is a more than 99.5% accurate version of the autographs–the original writings.