Bart Erhman claims that the major doctrine of the Trinity is removed if this passage is missing from the majority of the earlier manuscripts and that indeed there is major doctrinal change with some variations. However when one actually thinks about the doctrine of the Trinity, we don't hardly think of this passage as it is removed from modern translations. The doctrine of the trinity is still to be found in the bible regardless if this passage is present or not. For example we would use the passages that say there is one God, that Jesus is God, that the Father is God and that the Holy Spirit is God and thus you have the doctrine of the Triune God. The Trinity as Bart Erdman suggests is not a fabrication around AD 1600 when the 1 John passage started to be included in the manuscripts. If one wishes to be completely dogmatic about this particular passage the early Church Father Irenaeus actually quotes the missing passage in 1 John 5:7, so one might argue it got left out of the original writings. Either way the doctrine of the Trinity still stands and is taught in the bible, regardless of the passage in question and thus no doctrine is changed because of variations.