The gravitational pull of the moon ensures that the earth remains in a constant position on its axis, despite the way it is moving around the axis. Without the moon, the earth would not be able to continuously rotate and it would be uninhabitable.
Jupiter and the sun both have gravitational pulls which have the possibility of affecting the earth. These gravitational pulls could cause the earth to be constantly changing positions and would make the purpose of the axis of the earth defunct. These pulls could cause tides to change and would make the climate on the earth unstable. The gravitational pull of the moon is able to intercept these pulls and help the earth maintain a constant position on the axis.
It is important to note that the moon is perfectly positioned to the earth to help it maintain a constant position. If it were even slightly farther away or Jupiter were slightly closer to the earth, the pulls of the moon would not be effective. They would be so ineffective that the position of the earth could vary as much as 90 degrees. Mars is an example of what earth would be like without the large moon and the accompanying gravitational pulls.