Matt 17:19-20 Then the disciples came to Yeshua (Jesus) in private and asked, "Why couldn't we drive it out?" He replied, "Because you have so little faith. I tell you the truth, if you have faith as small as a mustard seed, you can say to this mountain, `Move from here to there' and it will move. Nothing will be impossible for you."
A mustard seed is a very tiny seed, Yeshua disciples did not have faith enough to command the demons and cast them out of the boy.
Matt 17:21 However, this kind does not go out except by prayer and fasting."
As believers in Yeshua, we are given power over demons too.
Mark 16:15-18 And He said to them, "Go into all the world and preach the gospel to every creature. He who believes and is baptized will be saved; but he who does not believe will be condemned. And these signs will follow those who believe: In My name they will cast out demons..."
Casting out demons is certainly not an every day occurrence. Most of us will never encounter this type of problem. Here Yeshua tells them this was the type of demon that was not going to leave easily, it would be necessary for the disciples to pray and fast, seeking G-dís strength to cast out the demon.
Matt 17:22-23 And while they abode in Galilee, Yeshua (Jesus) said to them, The Son of man will be betrayed into the hands of men. And they will kill Him, and the third day He will be raised again. And they were exceeding sorry.
Yeshua makes a short-term prophecy, which confirms that He was a true prophet for it did come to pass.
Matt 17:24 And when they were come to Capernaum, they that received temple tax came to Peter, and said, Does not your master pay the temple tax?
The temple tax was a Ĺ shekel collected from all males over 20 years old one a year for the up keep of the temple.
Exodus 30:13-14 This they will give, every one that passes among them that are numbered, half a shekel after the shekel of the sanctuary: (a shekel is twenty gerahs:) an half shekel will be the offering of the L-RD. Every one that passes among them that are numbered, from twenty years old and above, will give an offering to the L-RD.
Matt 17:25 He said, Yes. And when he was come into the house, Yeshua (Jesus) anticipated him, saying, What do you think, Simon? of whom do the Kings of the earth take customs or taxes? From their own children, or from strangers?
Matt 17:26 Peter said to him, from strangers. Yeshua (Jesus) said to him, then the sons are free.
Here Yeshua declares His Kingship. Yeshua being the Son of G-d should have been exempt from paying the tax but paid not only for Himself but also for Peter.
Matt 17:27 Notwithstanding, lest we should offend them, you go to the sea, and cast a hook, and take up the fish that first comes up; and when you have opened his mouth, you will find a piece of money: take that, and give to them for me and you.
Amazing. How could he do such a thing? One of His divine attributes is omniscience. The fact that G-d came down as a man makes sense when you understand we are made in His image.