Why did the holy spirit came upon Jesus as a DOVE and upon his disciples as FIRE ?

Please reread the text, it states "LIKE" a dove. The Holy Spirit did not take the form of a dove, that's blaspheme. In the scriptures, the dove is pictured as domesticated or a "clean" bird which is very selective in what it does and eat. This represents sustention of life meaning Christ the Life Giver and Sustainer.

4 In Him was life, and the life was the light of men. John 1:4

36 He who believes in the Son has everlasting life; and he who does not believe the Son shall not see life, but the wrath of God abides on him.” John 3:36

39 You search the Scriptures, for in them you think you have eternal life; and these are they which testify of Me. 40 But you are not willing to come to Me that you may have life. John 5:39-40

48 I am the bread of life. 49 Your fathers ate the manna in the wilderness, and are dead. 50 This is the bread which comes down from heaven, that one may eat of it and not die. 51 I am the living bread which came down from heaven. If anyone eats of this bread, he will live forever; and the bread that I shall give is My flesh, which I shall give for the life of the world.” John 6:48-51

63 It is the Spirit who gives life; the flesh profits nothing. The words that I speak to you are spirit, and they are life. John 6:63

Now the fire. In the scriptures, the LORD God is always represented as Holy hence a REFINER'S FIRE. Let's read the text: 2 And suddenly there came a sound from heaven, as of a rushing mighty wind, and it filled the whole house where they were sitting. 3 Then there appeared to them (WHAT IS IT THAT APPEARED, FIRE? NO! IT WAS) divided tongues (what appeared was a known language spoken by Jews from multiple nations that were present in Jerusalem for the festival as required by the Law of Moses), AS OF FIRE (it wasn't fire, it was languages that caused them to speak in the purity of a language that they did not know nor understand but was known and understood by those Jews who were from that particular country where that particular language was spoken. It was not gibberish!), and one sat upon each of them. Acts 2:2-3

Those disciples were purified by the very presence of God in the form of the Holy Spirit to offer up to God an acceptable offering in righteousness. This was in opposition to the RITCUAL OFFERINGS being made during the entire festival by the RELIGIOUS Jews. God was saying this is the offering I desire, one that comes directly from Me through you, not your stupid wicked evil self-serving manmade religion!

3 He will sit as a refiner and a purifier of silver; He will purify the sons of Levi, and purge them as gold and silver (Why O Lord God, holy, righteous, just, and true are You purifying them?), THAT THEY MAY OFFER TO THE LORD AN OFFERING IN RIGHTEOUSNESS. Malachi 3:3

3 The refining pot is for silver and the furnace for gold, but the LORD tests the hearts. (The Lord only tests the human spirit for SALVATION not your behavior. He judges the behaviors of born again believers and the unbelievers alike! He is holy!) Proverbs 17:3

9 Oh, let the wickedness of the wicked come to an end, but establish the just; For the righteous God tests the hearts and minds. Psalms 7:9

5 The LORD tests the righteous, but THE WICKED (not their sins) and THE ONE (the individual) who loves violence HIS (God's) SOUL HATES (This is for those who falsely state that God loves everyone. Not according to the scriptures.). Psalms 11:5

18 I said in my heart, “Concerning the condition of the sons of men, God tests them, (why LORD?) that they may see that they themselves are like animals.” Ecclesiastes 3:18

24 Therefore the Lord says, The LORD of hosts, the Mighty One of Israel, “Ah, I will rid Myself of My adversaries, and take vengeance on My enemies. 25 I will turn My hand against you, and thoroughly purge away your dross, and take away all your alloy. Isaiah 1:24-25

7 Therefore thus says the LORD of hosts: “Behold, I will refine them and try them;
For how shall I deal with the daughter of My people? Jeremiah 9:7

35 And some of those of understanding shall fall, to refine them, purify them, and make them white, until the time of the end; because it is still for the appointed time.
Daniel 11:35

10 Many shall be purified, made white, and refined, but the wicked shall do wickedly; and none of the wicked shall understand, but the wise shall understand. Daniel 12:10

9 I will bring the one-third through the fire, will refine them as silver is refined, and test them as gold is tested. They will call on My name, and I will answer them. I will say, ‘This is My people’; and each one will say, ‘The LORD is my God.’” Zechariah 13:9

In order to understand the scriptures, one must take the entire counsel of God, meaning to read the entirety of the word of God and assemble it according to the entirety of its revelation. The entire theme of the Bible is three fold:
1. God created all things for the purpose of revealing Himself through His attributes.
2. In order to truly reveal the fullness of His attributes, God understood that evil and sin must be allowed else no one would fully understand how merciful, longsuffering, loving, kind, just, righteous, sovereign, holy, forbearing, and wise He really is. Hence God instituted a reconciliation plan before creating anything. That plan is the sacrifice of Himself upon the cross in the person of His Son, Christ Jesus the Lord.
3. God was determined to reveal His Redeemer, the Lord Jesus Christ.

If one would read the scriptures with these three things in heart and mind then the scriptures will come alive and all you will see is Christ.

Unfortunately, most read the Bible to resolve their earthly problems, obtain some kind of physical or material so-called blessing, or with the pretense that God will favor them because they behave in a superior morality than others. What utter nonsense!

The LORD God isn't impressed by men nor the deeds of men. He is only interested in what pleases Himself for the praise of His own glory and the glory of His grace. What pleases Him is His Son. If you are in Christ then you please God because Christ pleases God. If you are not in Christ then it is impossible for you to please God because you are not a member of the body of the only One who can please God.

3 Blessed be the God and Father of our Lord Jesus Christ, who has blessed us (the born again believer) with every spiritual (not physical) blessing in the heavenly places (not on this earth) in Christ (God's blessing is Himself and His Son, what more can He give you!), 4 just as He chose us (wait, what?!!! God chose us? That what it states, you cannot chose Him because dead people cannot make choices! Dead in trespasses and sins. Do You mean that it wasn't because I was smarter than others to decide to chose You Lord? Yes, especially that.) in Him (only in Christ. When did You do this Lord?) before the foundation of the world (Were you there with your good behavior to assist the Lord?), (why did You to this prior to creation Lord?) that we should be holy and without blame before Him in love (Whoa!! That is wonderful! Thank you, LORD!), 5 having predestined (Lord, don't You realized that most people hate that word predestined? You are not being politically correct. This must be a mistake.) us (You mean born again believers? Yes. Wow!) to adoption as sons by Jesus Christ to Himself, ACCORDING TO THE GOOD PLEASURE OF HIS WILL (Do you mean to tell me it wasn't because I'm a good person and morally superior to others? Yes, especially that. I did it for My Own will. Why would you do that, LORD?), 6 to the praise of the glory of His grace (That's why. Anymore questions?), (and oh, just so you will know, I did it because of this too.) by which He made us accepted (I cannot accept you any other way but) in the Beloved (My Son Jesus). Ephesians 1:3-6

There you have it folks.
21 For He made Him who knew no sin to be sin for us, that we might become the righteousness of God in Him. 2 Cor. 5:21