Have you ever wondered why our solar system is very near a perfect disk instead of a blob of planets in willy-nilly positions? Well, I have. So I will try to give you a logical answer. Our star, the Sun, formed out of dense cloud of gas and dust. The stuff in that cloud kept bouncing off each other and sometimes a couple of those particles stuck together. The more particles that it bumped into the more that stuck to it so it grew bigger and in doing so, its gravity started to increase and thus it attracted more and more particles until it got to be a very, very huge glob. This glob then had developed that awesome force of gravity which then attracted more and more stuff.
It got so big that it imploded into a disk and became dense enough at the center to start a thermal nuclear explosion. This, I believe, is what ignited that blob into a star, and this particular star became our sun. The disk of dust around it had denser areas that coalesced which in time formed the planets. Because the planets were formed from this disk, they are in the same plane or very near the same plane.
OK, you say that sounds logical, but why did it implode into disk instead of a smaller ball. That is because way back when it all started, the big ball of gas and dust had so much gravitational pull that the ball squashed down to a disk. Of course, I believe that it had divine guidance. OK, that is the way I understand what happened. If any of you have a different theory, please let us all know.