Q. Which is more important, Rosh HaShanah or Yom Kippur?
A. Which is more important? They both are. Rosh HaShanah focuses on what we could be, and Yom Kippur on what we actually are.
On Rosh HaShanah we rise to a level where the world is beautiful and sin does not exist; on Yom Kippur we come down to earth and recognise the reality that we have actually sinned.
We need both festivals. If all we had was Rosh HaShanah, we would imagine that there were no problems; if all we had was Yom Kippur, we would imagine that all that exists are problems. One day is the foil to the other.
We need to dream on Rosh HaShanah, and to wake up on Yom Kippur. We need to recognise on Yom Kippur that there are real problems, but we need the Rosh HaShanah message that if we work hard enough on the vision we can build a world without problems, a civilisation without threats, and human beings without moral lapses.