"And it came to pass, that, while Apollos was at Corinth, Paul having passed through the upper coasts came to Ephesus: and finding certain disciples, He said unto them, Have ye received the Holy Ghost since ye believed? And they said unto him, We have not so much as heard whether there be any Holy Ghost. And he said unto them, Unto what then were ye baptized? And they said, Unto John’s baptism. Then said Paul, John verily baptized with the baptism of repentance, saying unto the people, that they should believe on him which should come after him, that is, on Christ Jesus. When they heard this, they were baptized in the name of the Lord Jesus. And when Paul had laid his hands upon them, the Holy Ghost came on them; and they spake with tongues, and prophesied. And all the men were about twelve." (Acts 19:1-7).

1) What caused Paul to question whether they had received the Holy Spirit?
In 1Thessalonians 3:10 Paul writes that he wants to see their face to see what was still lacking in their faith.

Paul also wanted to see them face to face, but let's look at the interpretation that he wanted to see their face to see how it goes spiritually.

Our faces are the window of the heart. A person that's upset can be seen on his face. An angry person has the nickname of having the eyes of a mamba snake.
So too if a person has a grudge you see it on the face. If you go and visit murderers in jail, you see murder on their faces.

Some argue that God only looks at the heart and not on the outside.

John Bunyan said "yes God looks at the heart but we mortals look at the outside to judge the state of the heart".

The inner heart is not invisible but exposed.

So Paul saw something that moved him deeply when he saw them. What comes out of the mouth exposes the inside. Some say "I just spoke", but Jesus said we will have to give account for every idle word spoken.

God spoke to Cain's about his murderous expression on his face.

2). What did Paul saw in them? Maybe their behaviour and treatment of each other. He could see they're not truly one in spirit - like the disciples quarreled about who was the greatest they too wanted to be noticed.

If the Holy Spirit is in us He leads us into all truth and sanctifies us and reveals God to us.

Have you received the Holy Spirit in His fullness since you believed? Have you received the baptism of fire - to be baptised into the Holy Spirit.

You cannot repent or be born again without the Holy Spirit.

So it is obvious that the Holy Spirit had been working in them but they did not recognise Him.

So it is possible that the Holy Spirit can work through you without you being baptised into the Holy Spirit.

"But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his." (Romans 8:9).

Jesus breathed on the disciples saying, "receive the Holy Spirit", yet Pentecost only took place later.

Example: When you pour Pepsi of Coke into a glass full of ice, the glass will be filled, but once you've drunk everything you will see that the glass was actually only half full of Pepsi / Coke - the rest was ice.

So one may have the Holy Spirit but not in His fullness.

Someone who forgives but cannot forget and so holds a grudge grieves the Holy Spirit.

If you continue to grieve Him eventually you will quench Him. It's like quenching a fire. You will extinguishing Him in your life.

So the Word says, "do not quench the Holy Spirit". It's heartbreaking if you meet someone and realises that he has quenched the Holy Spirit.

David grieved the Holy Spirit but when he realised it he repented.

What kind of a life does the Holy Spirit have in your life?
Maybe He speaks to you but you ignore Him and eventually He will leave you.

To us the Holy Spirit comes like a fire for there are lots of rubbish in our lives that need to be burnt and done away with.
At Pentecost the first thing He did was to touch their tongues.

The most wicked member of our body is the tongue. We think sexual immorality is bad and it is, but the tongue is worse.

The Bible goes so far as to say that the man who can control his tongue is the perfect man.

Many people are confused with regards to baptism always thinking of water baptism. But Jesus even spoke about His baptism of suffering. So it can refer to different things. So don't be superficial about baptism.

The Holy Spirit will also come from a completely different angle to what you expect.
In Isaiah the Lord says, "your ways are not My ways".

If you want to receive the fullness of the Holy Spirit, you need to commit yourself totally to Him. Also don't prescribe to Him which gifts He must give to you. Leave that over to Him.

In this particular case these 12 spoke in tongues not because they insisted upon it but because it was from God; it was His will.

They also prophesied. Today many claim to prophesy but it's fortune telling - telling you your future. Prophesy is speaking God's mind - saying what God says. The best kind of prophesy is publicly expounding the Word of God.

Finally the Holy Spirit is holy - He comes with holiness.

Before the Lord ascended into heaven He said you will receive the Holy Spirit to receive power to be My witnesses, my martyrs; that you will be able to rather die than speak a lie or flirt around.