If we love the brethren, we know that we have passed from death to life  -  1 John 3:14

We know that we have passed from death unto life, because we love the brethren. He that loveth not his brother abideth in death.

As soon as we are saved, our attitude towards other believers change. An individual who does not love other believers, though they profess to be a Christian, is still without Christ.