Acts 19:2

"[Paul] asked them, "Did you receive the Holy Spirit when you believed?"
They answered, "No, we have not even heard that there is a Holy Spirit."

How is it that someone can be a believer and while having never received or even heard of the Holy Spirit?  Doesn't the Holy Spirit indwell all believers?  The text makes clear that these were disciples, but does not make clear whose disciples they are.  They were baptized once with the baptism of repentance, but the text then goes on to say that they were re-baptized in the name of the Lord Jesus.

It seems that their first baptism was inadequate and whoever discipled them left the job undone.  These were nominal Christians.  John's baptism was good, but it was insufficient for salvation.  Some others had come before Paul to Ephesus and preached only a small part of the good news of Christ and went on their way, unknowingly leaving behind a remnant of shallow half-Christians who only think they are saved.

How much of a burden then lies on us, as members of Christ's body, to preach the whole gospel in order to make whole Christians?  We have a charge to make disciples of all nations, not just to baptize but to teach them to obey all things Christ has commanded.  Paul taught in the area two years, making sure all have heard the message and were rightly taught before he moved on.  We ought follow him as he follows Christ.

Revelation 3:15-16

"I know your deeds, that you are neither cold nor hot. I wish you were either one or the other! So, because you are lukewarm—neither hot nor cold—I am about to spit you out of my mouth."

I have heard these words preached twice in my life.  The first time I was a teenager in Catholic Mass and the message went something like this, "God wants you to be so completely for Him or completely against Him.  Those who are lukewarm he will vomit out of his mouth (i.e. reject as something vile)."  I said to myself, "If God is this divisive, then I will be against him.  I do not know him well enough to be for him."

The second time I heard the message, I was a young man who had just received Christ in college and joined a new church.  It went like this, "God wants you to be useful.  Cold water is good for some things and hot water is good for others, but there really is no use for lukewarm water."  The message was healing.  It was gospel.  This is the difference in proper study of God's word.

So my friends, be careful of every single word you say.  Think theologically.  Think about what exactly it is you are saying about God lest you speak lies and slander His holy name by which you are saved.  You never know who might be listening lest you cause one of these little ones to stumble.