Jesus Christ actually lived in history, was put to death on the cross, and rose from the tomb three days later to minister and instruct his disciples. That was the straightforward testimony of the brave and simple men who were his disciples, the testimony for which they were willing to die cruel deaths.
Islam denounces all of this as a vile heresy, condmens it as bald fiction, and calls for the death of any Muslim who would profess a belief in it.
Islam is antichrist.
There was a late holdover of Arianism in Christianity. The Visigothic Arians had developed certain liturgical peculiarities, along with the theological heresies. When they converted to true Christianity a compromise was made for their liturgical ideas, which became the Gothic Rite of the Church. Many true Christians who had been persecuted by the Arians objected to this and would not accept the Gothic Rite.
Most Christians felt that this liturgical concession was a small price to pay to finally destroy the vile Arian heresy. After Spain was conquered by the Moslems at the end of the 7th century, it lacked the strength to maintain the seperate Gothic Rite, which eventually disappeared, which is why Spanish Christianity was essentially identical with the rest of Western Christianity.