Jesus was sprinkled because the baptism he received from John was an annointing for a very special high priesthood "after the order of Melchesideck" where he became the great High Priest for the entire world by eliminating the Aaronic priesthood and establishing a better priesthood under a new covenant. See also: Heb. 7:11-17; Heb. 7:21- 8:7; Heb. 9: 23-26; Heb. 10: 12-22; Hebrews 5:5-6 (ESV) So also Christ did not exalt himself to be made a high priest, but was appointed by him who said to him, "You are my Son, today I have begotten you";  as he says also in another place, "You are a priest forever, after the order of Melchizedek." We read that it was at his baptism that God aknowledged His Son: Luke 3:22 (ESV) and the Holy Spirit descended on him in bodily form, like a dove; and a voice came from heaven, "You are my beloved Son; with you I am well pleased." It is evident that John's baptism of Jesus was in fact an annointing for this great "high priesthood"? John said, "for this purpose I came baptizing with water, that he might be revealed to israel" John 1: 31. " Then Jesus came from Galilee to the Jordan to John, to be baptized by him. John would have prevented him, saying, "I need to be baptized by you, and do you come to me?" But Jesus answered him, "let it be so now, for thus it is fitting for us to fulfill all righteousness". Then he consented." John knew that Jesus needed no repentance like the rest of his candidates for baptism and the one thing that convinced him to baptize Jesus was the request to "fullfill all righteousness" This meant the fullfilling of the Law required for the annointing of priests found in Exodus 40: 11-12 and Num. 8:6-7. After Jesus was baptized, we are told that he commensed a ministry of teaching and preaching in and around the temple, a prerogotive normally given only to priests: Luke 20:1-7 (ESV) One day, as Jesus was teaching the people in the temple and preaching the gospel, the chief priests and the scribes with the elders came up  and said to him, "Tell us by what authority you do these things, or who it is that gave you this authority."  He answered them, "I also will ask you a question. Now tell me,  Was the baptism of John from heaven or from man?"  And they discussed it with one another, saying, "If we say, 'From heaven,' he will say, 'Why did you not believe him?'  But if we say, 'From man,' all the people will stone us to death, for they are convinced that John was a prophet."  So they answered that they did not know where it came from. John himself, being a priest, had the authority to annoint Jesus as priest. We know that Jesus followed the law concerning circumcision and the various feast days, and was baptized by John at age 30, the normal age for the annointing of priests, and by the authority of his baptism he conducted his ministry in the temple. John was both priest and prophet . His father was a priest named Zechariah, of the division of Abijah, and his mother was Elizabeth from the daughters of Aaron. The Aaronic priesthood was handed down from father to son. It was while Zechariah was ministering in the temple that the Lord appeared to him and told him to name his son John. John's father and John himself were annointed for the priesthood from a basin located between the alter and the tent of meeting, a basin normally used to wash the hands and feet of the priests before they entered into the tent to minister. On the special occassion of a person called to the priesthood, they were annointed for the office by a baptism from this basin. Exodus 40:11-12 (ESV) You shall also anoint the basin and its stand, and consecrate it.  Then you shall bring Aaron and his sons to the entrance of the tent of meeting and shall wash them with water The Bible describes how these washings were to be done. John baptized by sprinkling and pouring because this was the law God gave and the only law he knew anything about. David said : "Purge me with hyssop , and I shall be clean, wash me and I shall be whiter than snow" (Psalm 51:7). The hyssop was a plant or weed that held a lot of water and was especially suitable for ceremonial sprinklings when dipped in water. Num. 19:18-19, "And a clean person shall take hyssop, and dip it in the water, and sprinkle it upon the tent, and upon the vessels, and upon the persons that were there, and upon him that touched a bone, or one slain, or one dead, or a grave: and the clean person shall sprinkle upon the unclean on the third day and on the seventh day." In Numbers 19:18 we read: "Because the water of separation was not sprinkled upon him he shall be unclean." Here is Gods command for the Levitical priests: Num. 8:7: " Thus you shall do to them to cleanse them: sprinkle the water of purification upon them" This is what John did at his baptisms probably using the hyssop weed. His manner of baptizing caused the Pharisees to think that he himself was Christ because the same book of law and prophecy that predicted his ministry as forerunner predicted that the Messiah would "sprinkle many nations" (Isa. 52:15). They even sent Jews, priests and Levites from Jerusalem to ask him if he were the Christ. John 1:25, "Then why are you baptizing, if you are neither the Christ , nor Elijah, nor the Prophet?" they asked." From this we know that Jesus was to come sprinkling and pouring with the Holy Spirit, while John was to come baptising with water. Matthew 3:11 (ESV) "I baptize you with water for repentance, but he who is coming after me is mightier than I, whose sandals I am not worthy to carry. He will baptize you with the Holy Spirit and with fire. Acts 10:43-47 (ESV) To him all the prophets bear witness that everyone who believes in him receives forgiveness of sins through his name."  While Peter was still saying these things, the Holy Spirit fell on all who heard the word.  And the believers from among the circumcised who had come with Peter were amazed, because the gift of the Holy Spirit was poured out even on the Gentiles.  For they were hearing them speaking in tongues and extolling God. Then Peter declared,  "Can anyone withold water for baptizing these people, who have received the Holy Spirit just as we have?" Acts 11:15-16 (ESV) As I began to speak, the Holy Spirit fell on them just as on us at the beginning.  And I remembered the word of the Lord, how he said, 'John baptized with water , but you will be baptized with the Holy Spirit .' It is amazing how water baptism and spirit baptism are always interconnected in the book of Acts, and since it is always true that Jesus "pours" the Spirit, we know that John poured the water becausse they are both baptisms , one symbolizing the other. " With water" could not mean immersion, if "with the Holy Spirit" means pouring.