There will always be those who cause divisions. These were people bringing in doctrines that were not the apostles' doctrine. It might be noted that the word, heresy, means "dissensions arising from diversity of opinions and aims" in the original Greek:

Romans 16:17 "Now I beseech you, brethren, mark them which cause divisions and offenses contrary to the doctrine which ye have learned; and avoid them."

Let God be true and every man a liar.

Apostles are given the responsibility of protecting the entire flock of God from the attack of the enemy, but with so many voices in the world, each one claiming to be the one that should be listened to, how can you know? You are responsible to be close enough to God so that you can tell the difference between false apostles and real apostles.

Read the complete definition of "Apostle."