"Love, love, love..." and the rest is history. John Lennon had a clear claim in mind when singing those lyrics with the Beatles. John Lennon's song "All You Need is Love" is, of itself, a very forthright claim, which Lennon has been known as in his life. He has always advocated that love is above all, trumps all, and "it's easy." However, judging by how humans are and what needs are, John is inferring that love is the most important thing we, as people and humans, have to attain and use. Simply put, "Love is all you need."
For John, love is a need that must be attained because it has a certain power to it that makes it so sought after by everyone. John sings "There is nothing you can know that isn't known. Nothing you can see that isn't shown. There's nowhere you can be that isn't where you're meant to be. It's easy." Knowledge, vision, and guidance all come with love. Everything is clear and understandable through love. Furthermore, love provides peace of mind because love brings vision and guidance, which bring direction and that is the mind not having to wonder about where to.
In John's eyes love is a need that is important to use. In the first verse he sings, "There's nothing you can do that can't be done. Nothing you can sing that can't be sung. Nothing you can say, but you can learn how to play the game. It's easy." It's easy because if you have love, all of these situations are solved. Love provides the strength to do, what can't be done; the courage to sing, which can't be sung; and the wisdom to adapt to different contexts.
Finally, this does bring some questions to mind to further the discussion on how great love is, such as: how practical is love, when opposition is so much easier? And, if love were to be accepted by everyone, what and how many problems would it solve?
John Lennon held love in such a high regard that, in his mind, love could fix the world. Which is the reason, while he sings: "All you need is love" Lennon also says: "All together now.... [and] Everybody." He wants everyone, the whole world, to accept this notion of love being the only thing you need. In the end, it is all you really need.