I can say that I like a challenge and you tell me it's painless
You don't know what pain is
Whoever Kendrick is addressing here, (competing rappers, the industry, a lover, his life, death?), is challenging him. Kendrick is prepared for what’s coming because of the events in his life leading up to this moment — everything else up to this point has been full of much more difficult challenges.
The “challenge” Kendrick means could be getting through to these empty-souled people and giving them a message. It’s difficult to try to make people listen deep into music these days but Kendrick is willing to try.
When he speaks at first, he would be speaking to the Lord, telling him that having discovered why he was on this Earth plus him liking a challenge, he was ready to poursue the aim God had gave him; spreading the Love, opening people’s hearts.
The word “painless” holds the meaning here:
Defeating his rivals is a painless exercise because it’s so easy
These rivals are painless — without pain — because they haven’t endured a life as challenging as Kendrick (“you don’t know what pain is”)
In the following, bars, “painless” relates to the metaphor of painting a picture/color blind — i.e. a window that is *pane-less"
The line also sounds like “you tell me it’s painless”. The person talking to Kendrick says the challenge head of him is painless, but Kendrick knows he doesn’t because that person has never dealt with this situation, (hence the later part, “You don’t know what pain is”).
To help improve the meaning of these lyrics, visit "Bitch, Don't Kill My Vibe" by Kendrick Lamar Lyrics and leave a comment on the lyrics box