This is an interesting passage that I have not really focused on specifically.
Early in Luke chapter 6, Jesus was up on the mountain praying the whole night (v. 12). This must have been an intense moment of focus on the future and dedication to His ministry as this was followed the selection of the twelve inner circle of disciples, named as apostles (v. 13). Jesus came down the mountain with them and stood in a level place to begin teaching the rest of His disciples and many people from around (v. 17) who came to hear and be healed (vv. 18, 19).
Jesus begins a discourse that parallels what is know as the “Sermon on the Mount,” which is also found in Matthew 5 - 7. The verses 39, 40 are oddly placed and some theologians note a point of somewhat discontinuity with the rest of the message. However, the context is still aligned with a theme of leadership and along the lines of Jesus’ teaching (cf. Mat. 10:23). From our modern perspectives, we mayhave an endless amount of resources at our finger tips, but that is our situation. For the audience of this discourse, the Jewish rabbi was the only source of information for his disciple. It would be exceedingly presumptuous for a disciple to claim to be above his teacher. Jesus’ use here was to highlight His command of love that the disciples needed to be fully trained in, and to be alert for spiritual blindness. That spiritual blindness was evidenced in the human teachers of that day (cf. Mat. 23:24), and the very next verses highlight the result of a blind and arrogant person trying to guide out of their own blindness (v. 41).
I hope that brief exegesis helps in some way. Let me know if I’ve not covered anything enough or if this spurs more thoughts.
Thanks for bringing up an interesting passage!
 Norval Geldenhuys, Commentary on the Gsopel of Luke in The New International. Commentary on the New Testament (Grand Rapids: Eerdmans, 1979) 213-214.
 Leon Morris, Luke in Tyndale New Testament Commentaries, vol. 3 (Leicester: Inter-Varsity, 1989) 146-147.