Hello there! :D
Martin Luther wrote the 95 theses for the Roman Catholic Church. He wanted to prove that the way they manipulated people and used Christianity as a political and financial benefit was wrong. That the pope and other religious figures were not communicating the real truth of Christianity but twisting it.
One of his theses states that he did it "out of love for the truth and from the desire to elucidate it." So I ould say 'truth'.
I hope this helps!
~kaikers