Because Calvin were in complete agreement /Sarc
http://lexloiz.wordpress.com/2009/01/15/john-calvin-and-martin-luther-%E2%80%93-some-differences/
http://confessionalouthouse.wordpress.com/2014/04/28/luther-vs-calvin-on-images/
Let's not forget about that whole predestination vs. self determination thing either. And how about that Faith alone?
Lets not leave out ole Zwingli either:
Luther- the bread and the wine are really the Body and the Blood of Jesus Christ, given for the remission of sins.
Calvin- Christ is spiritually present in the bread and the wind.
Zwingli- the bread and the wine are only symbolic and consumed as a memorial for Jesus Christ.
Who is it that doesn't understand Sola Scriptura?
Sola Scriptural is the biggest fraud ever perpetuated on Christianity.