A Christian cannot vote for Clinton for no other reason than she is actively promoting abortion and wants to withdraw the rights of religious groups to opt out of funding these. Abortion is evil, so then there is no rational way for a Christian voter, true to his faith, to vote for her. 

Planned Parenthood has called Clinton its “champion” and implied that she could replace President Barack Obama as the most pro-abortion president in U.S. history. Clinton has promised Planned Parenthood that she would repeal the Hyde Amendment and force taxpayers to fund abortions. She also promised to nominate U.S. Supreme Court justices who will ensure that Roe v. Wade and abortion on demand up until birth (and now "partial birth") remain the law of the land for years to come.