What do christians say about the following verse?

Indeed, they disbelieve and say, “God is the third of three (in a trinity),” when there is no god but one God. If they desist not from what they say, truly, a painful punishment will befall the disbelievers among them. Would they not rather repent to God and ask His forgiveness? For God is Oft-Forgiving, Most Merciful. The Messiah (Jesus), son of Mary, was no more than a messenger... (Quran, 5:73-75)