This is a poorly phrased question because it uses the ill-defined term “important”.
But it is one that is often asked so maybe it needs an answer.
The word “important” is used in many ways. If you value human life, then even an economically unproductive life is important. And even in strictly economic terms, a hunter-gatherer may survive by picking fruit and catching frogs without the need for any physical capital besides access to a productive environment (and perhaps the “intellectual capital” of information passed down from previous generations about what is and is not safe to harvest). So capital has not always been even economically more “important” than labour.
But in the *modern* world we rely very much on both accumulated knowledge and built infrastructure to enhance our productivity – so much so that anyone who has access to and control of these things that we call “capital” can easily purchase any necessary labour from those who do not “own” the capital by offering them a small share of the product which will, though tiny, nonetheless vastly exceed what they could produce for themselves without access to that capital.
This raises the obvious question of in what sense it is in any way appropriate, fair, or right that some few people should by birth be assigned a hugely disproportionate share of the world’s accumulated capital while the rest are reduced to bargaining their increasingly unnecessary labour for a tiny share of the product.
So far as I can see, that obvious question has an obvious answer. It’s not! There is no argument that I can accept which justifies the present state of affairs and it’s long past time to fix it.
Source: (328) Alan Cooper’s answer to Why is capital more important than labor? – Quora