You take it for granted that Jesus peac upon him did say he is the son of God - or did he say he's God , anyway - and we believe in Quran which tells us he was a prophet . We also believe in Quran which says that the peopl eof the book corrupted their scriptures after they were intrusted to them . Thus , you shouldn't ask why we don't belive in something that Jesus said because we DON'T believe he said it .