“therefore” (KJV) is a reference to #3:22, the work of John the Baptist, and the jealousy of John’s disciples.

“the Lord” (KJV) was used in an ordinary form of address much as our “sir” but was sometimes applied to God with great reverence.  During His earthly ministry, Jesus was usually addressed as “Jesus” or “Rabbi” (teacher) but sometimes as “Lord.”  In the latter case, the usage was normally in the polite form of address and not in reverence as deity.  At times, however, the term “Lord” was used of Him in the reverential sense as in John 6:68, 20:28.

John 6:68  Simon Peter answered him, “Lord, to whom shall we go? You have the words of eternal life.

John 20:28  Thomas said to him, “My Lord and my God!” 

The Pharisees had already expressed an interest in the work of John the Baptist and it is not unusual that they would be very interested in someone who was receiving even more attention from the crowds than John.  Why, do you think?