I mean you need to hear this, love is not just a verb
It's you looking in the mirror, love is not just a verb

from Kendrick Lamar (Ft. Drake) – Poetic Justice Lyrics on Rap Genius

Meaning

Love is not just sex, and love is way more than an action or feeling, it is many things.

Kendrick uses 2 analogies to cut some of the ambiguity: It’s looking in the mirror, loving thyself, and it’s actively looking for it, rather than waiting for it to come.
*In other words, you have to do some soul searching to find out what it means to you personally.

Another track from GKMC, “Real,” expounds in its entirety on this motif of what love is and is not, with the key connecting lyric being:

But what’s love got to do with it when you don’t love yourself

Love is not just something that happens, in order to really love another person, you have to be willing to be honest about who you are, what you do, and why you do it. If you’re not willing to own what you do and who you are you cannot truly love a person fully, it’s selfish. Love doesn’t just happen, you have to be open to it.

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