New Testament ideas:
James 1:8 he is a double-minded man, unstable in all his ways.
Revelation 3:15 I know your works, that you are neither cold nor hot. I could wish you were cold or hot.
Matthew 6:24 No one can serve two masters; for either he will hate the one and love the other, or else he will be loyal to the one and despise the other. You cannot serve God and mammon.
Matthew 5:8 N Blessed are the pure in heart, For They shall see God.