What a man believes is ultimately going to determine his life.  A man who is loose in doctrine eventually becomes loose also in his life and in his behaviour.

And I do not hesitate to say that the church of God on earth is as she is today primarily because of the looseness of belief in doctrine which entered in the last century, and has continued to the present time.

You cannot separate these things; doctrine and conduct are indissolubly linked.

D. Martyn Lloyd-Jones