Newton's Law of Motion states that each time a is force applied to an object, that object applies an equal force back in the opposite direction. For example: Dave is standing. I push him. Now, since Dave is strong, my push does not bowl him over, and I can feel the force of his resistance as I push. Push and resistance: two opposing forces at work thousands of times each day.
It's taught that any principle in the physical world is merely a representation of what is happening in the spiritual world, the world of the unseen that is shaping our lives "behind the scenes." So, what, does that mean G-d is having a wrestling match with the angels? Possibly, but more to the point, our world is a place where each action has a reaction. Granted, the relationship between the two is usually hard to understand. An evil dictator takes power and he's allowed to remain there for years on end. A small rodent pops out of the ground on February second and the world awaits with baited breath to determine the weather forecast. It turns June and Maine is hit with a blizzard. But though the results of our actions are usually unpredictable and even opposite of what we expect, we can't function in a world without opposites.
In the Talmud on Yom Kippur there's a discussion about the two goats brought as sacrifices on Yom Kippur. A question is asked: What if the high priest makes a mistake while sacrificing the goat that atones for the priests? According to Rav Nachman, the high priest must redo the service with a new goat. "Well," demands Rava, "do you intend to bring forth a whole flock of goats?" Because each time the high priest starts over, two goats (not just one) are brought and lots are picked to see which one will atone for the priests and which one for the people of Israel. They come in pairs. There's no avoiding that, even though only one goat needs to be replaced.
Yom Kippur is a day when we come clean. We come before our Creator - the Creator of the world - without any excuses, without any pretense at knowing better than G-d. The day is a tikkun (a way to make reparation) for what happened in the Garden of Eden. What happened when we ate from that tree of "knowledge of good and evil?" What changed? When we ate, we became separate. Until that point, our will and G-d's were one. We wanted to come close to G-d, to grow, and G-d wanted to come close to us. After we made our choice to take, to put our desire above G-d's, we couldn't stay in the Garden anymore. We didn't have a place in that world of total harmony. Our choice took us to a new world, this world where knowledge is acquired by way of opposites. I know I'm having a good day when I DON'T feel tired. I know I'm full when I'm NOT hungry. I get hurt when I DON'T feel love.
That's what Rav Nachman and Rava were arguing about. In this world of choice, there must always be an opposite, a road we don't go down. Each choice we make must show us the direction we could have taken. We all know the old joke about the two Jews on a desert Island who built two separate shuls so that there would be a shul they "wouldn't be caught dead in." Right now we need that distinction to be clear. But it's not the way to bring completeness into our life. The only way to do that is to return to the Garden. In Pirkay Avot (Ethics of our Fathers), Raban Gamliel stresses the need to make our will like G-d's will, so G-d will make His will like our will. The only way to get beyond living in a world of reaction is to return to a world where our choice is G-d's choice. Sure, that opposite choice will still exist, but ideally we won't need it.
Newton had another law of motion. It states that an object in motion will stay in motion until acted upon by an outside force. May we always be in motion, moving closer to whence we came, bridging the gaps between what is and what we truly desire.