2 John 1:9

Anyone who runs on ahead and does not remain in the doctrine of Christ (that is, one who is not content with what He taught), does not have God; but the one who continues to remain in the teaching (of Christ does have God), he has both the Father and the Son. 

When Jesus died on the cross, it was a finished work. The example for the followers of Christ has been clearly set and does not need to be modified. Our knowledge of the word and the works of Jesus keep us from being deceived and pulled away from Jesus. We are to test the spirits and the preachers to make sure what they say lines up with the word of God.