“O faithless society, how long will I be with you? ...” (Mark 9:19)

“O faithless society, how long will I be with you? How long will I have to bear you? Bring him to me.” (Mark 9:19)
Here is the context of the situation and the events that took place according to the Lost Gospels of Jesus:
Then when he came towards his students he saw a great crowd surrounding them – and the scribes were questioning them. Then immediately after they saw him, all the people were greatly astonished and ran to him, joyfully greeting him. Then he asked the scribes, “What are you asking them?” Then someone from the crowd responded, saying, “Master I have brought to you my son, who has a spirit that makes him mute. And whenever it seizes him, it throws him onto the ground and he foams at the mouth and grinds his teeth – and he is wasting away. I told your disciples to remove it and they couldn’t.” Jesus responded by saying, “O faithless society, how long will I be with you? How long will I have to bear you? Bring him to me.” (Mark 9:14-29)


Who is Jesus admonishing?

This event illustrates that Jesus is admonishing these people for not having faith in God. These included temple scribes, Jesus' students, and others from the community. They were all convinced that only Jesus could cure the man.

The Greek word translated to "faithless" is ἄπιστος (apistos). Many versions have translated this word to "unbelieving," but the word means "unfaithful" and "faithless" according to the lexicon, as well as, "without trust in God."

Thus we can know that Jesus is not speaking of believing in him. He is standing in front of them. They all certainly believed that Jesus existed. And they also believed that Jesus could heal the body and cast out demons because they had observed him doing this. Plus the context of the conversation related to Jesus' reaction to the fact that his disciples could not cast out a demon - as the man said:
"I asked your disciples to drive out the spirit, but they could not."
This generated Jesus' statement about them being faithless.

Then after the man and his son were brought to him, Jesus told the man:
“If you will only have faith – everything is possible for one who believes.” (Mark 9:23)
So what kind of faith and belief is Jesus speaking of here?

Is this about trusting in God?

In the exchange with his students before the man and his son were brought to him. He is not speaking of them trusting in Jesus. He is speaking of their lack of trust in God.

We find this evident when Jesus said:
“This kind will come out only by prayer and fasting.” (Mark 9:29)
Who is Jesus speaking of praying to? To the Supreme Being.

We also find various other verses indicating that Jesus frequently prayed to the Supreme Being:
But Jesus would often withdraw to the wilderness to pray. (Luke 5:16)
Then he withdrew from them – about a stone’s throw away. He knelt down and began to pray: “LORD, if it pleases You, take this cup away from me, but let Your will – not mine – be done.” (Luke 22:41-42)

He was struggling and praying very earnestly, and his sweat became like drops of blood falling to the ground. (Luke 22:44)

After Jesus spoke these things, he lifted his eyes towards the heavens and prayed (John 17:1)
Jesus also prayed for his students:
"Yet I have prayed for you so your faith doesn’t fail you.” (Luke 22:32)
These verses and others make it clear that Jesus frequently prayed.

Who did Jesus pray to?

Praising Jesus and praying to Jesus are nice, but ignoring the very person Jesus himself prayed to is offensive.

As such, they also ignore the most important instruction of Jesus:
"Love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength.’" (Mark 12:30)
While there is nothing wrong with praying to or loving or believing in Jesus, to do so while ignoring the very Person (God) who Jesus came to introduce to us is to offend Jesus. We find this confirmed directly by Jesus:
"Not everyone who says to me, ‘lord, lord,’ shall enter the sanctuary of the spiritual realm – only one who does what pleases my LORD in the spiritual realm. Many will say to me at that time, ‘Master, did we not prophesy in your name and in your name cast out demons, and in your name perform many miracles? And I will say to them, ‘I never knew you: Get away from me, you who practice wickedness.’" (Matt. 7:21)
Thus we find that Jesus is actually offended by those who declare their allegiance to Jesus while ignoring the Supreme Being.

This is also why Jesus is so disgusted with these people. He calls them ἄπιστος (apistos) because they were not trusting in the Supreme Being. They were not relying on God.

Certainly, they accepted Jesus' existence and accepted that Jesus could heal. That's why the man approached Jesus in the first place.

But we can see from two angles that Jesus admonished them for not trusting in God. This, together with Jesus' own admissions and actions, confirms that the Supreme Being was responsible for all of the healings that transpired, including this one.

Jesus was channeling the healing ability of the Supreme Being because he is God's representative. He is loving God and serving God. Jesus is doing what pleases God, so there is a oneness of will and desire between them - not that Jesus is God. Jesus confirms this elsewhere:
“My teaching is not mine, but comes from He who sent me." (John 7:16)