Here John the Baptist is testifying of the ministry he received from God. He is telling us that the words which he spoke concerning Jesus was given to him by God. John was not speaking from his own mind or making up some philosophy. The words he spoke were given by God because God was now introducing His Son to the world.
(Mark 13:11 KJV) But when they shall lead you, and deliver you up, take no thought beforehand what ye shall speak, neither do ye premeditate: but whatsoever shall be given you in that hour, that speak ye: for it is not ye that speak, but the Holy Ghost. Mark 13:11 speaks of the persecution which believers will face during the New Testament age but the principle contained in this verse is applicable to all believers including John. John was to preach the word which God gave him concerning His Son and the true believer is to proclaim the true word of God and we are not to change anything but preach the words which God gave by inspiration. The second half of this verse speaks about receiving the Holy Spirit by measure. This means that the Holy Spirit would empower us in certain situations when needed and would relax His indwelling when we are in rest mode. As believers, we have received the fullness of the Holy Spirit and we are not given the Holy Spirit and His power according to the day we are having. We are always in the fulness of the Holy Spirit. (Eph 1:3 KJV) Blessed be the God and Father of our Lord Jesus Christ, who hath blessed us with all spiritual blessings in heavenly places in Christ: Eph. 1:3 teaches us that we have been blessed with all spiritual blessings which means nothing has been withheld or measured.In the last phrase the translators had added two words which are not in the Greek but add proper meaning to the phrase, “unto him.” Just as in old times whether it be the prophets or the Apostles or any believer, we have the Holy Spirit in measure, yet in the fullness, according to the spiritual gifts He places in us. In contrast, Christ has the fullness of the Holy Spirit without any type of measure in any situation or ministry. Just to summarize, we have the Holy Spirit in measure but unto Him, that is, Christ, He has the fullness without any measure or limitations. A measure denotes some type of limitation and that would indicate we are limited because we do not heal, raise the dead, or do other miracles even though we are indwelled by the Holy Spirit. Christ could heal, raise the dead, and do other miracles because the Holy Spirit in Him, was not by measure or limited in any way.