Does " clinched the matter" mean "grasped the conflict (in his mind)"?

Context:

Then tragedy struck. It came, not from outside but from within
his own mind, a mind fatally subverted and weakened by a funda-
mentalist religious upbringing that required him to believe that the
Earth - the subject of his Chicago and Harvard geological education
- was less than ten thousand years old. He was too intelligent not to
recognize the head-on collision between his religion and his science,
and the conflict in his mind made him increasingly uneasy. One day,
he could bear the strain no more, and he clinched the matter with
a pair of scissors. He took a bible and went right through it, liter-
ally cutting out every verse that would have to go if the scientific
world-view were true. At the end of this ruthlessly honest and
labour-intensive exercise, there was so little left of his bible that,
try as I might, and even with the benefit of intact margins
throughout the pages of Scripture, I found it impossible to
pick up the Bible without it being rent in two. I had to
make a decision between evolution and Scripture. Either
the Scripture was true and evolution was wrong or
evolution was true and I must toss out the Bible ... It was
there that night that I accepted the Word of God and
rejected all that would ever counter it, including
evolution. With that, in great sorrow, I tossed into the fire