Christians are indeed the light of the world.
The Lord is the source of the light which illuminates the Christian. This same truth applies to the salt of the earth. The shift from the second person plural to the third person singular is conclusive. John did baptize in the wilderness, and preach the baptism of repentance for the remission of sins. When the age of regeneration began on the first Pentecost after Jesus' resurrection, those who obeyed John's baptism while it was valid realized the remission of sins.