“The one who comes from above is above all; the one who is from the earth belongs to the earth, and speaks as one from the earth. The one who comes from heaven is above all.
Who is it that comes from above? Jesus. Who is it that is of the earth? John the Baptist and everyone else.
The teaching of the Baptist is important, but it is of earthly origin. Notice the repetition of “above all.” Jesus is absolutely preeminent; He is supreme over all men and over all things. This lends significance to the next verse(s).
Any quotation marks probably should have been closed after the previous verse. This and the following verses are probably the words of the writer of the Gospel of John.