Why does the Earths revolution cause a year?
Because the spinning of the earth causes the earth to resemble a top, the pole is virtually always oriented in the same direction (north pole facing the star Polaris, currently). So the effect of the tilt is that the sun reaches its high transit point in the sky and its low transit point in the sky (the solstices) once each during the period we call a year– one full revolution around our sun.
