The combinations, and movements, of these masses with gravitational, centrifugal and orbital velocity vector forces, create what we call the equatorial bulge, and thus, the axis of figure. If the Earth were a perfect sphere, there would not be such an axis.
The angular difference between the astronomical axis and the axis of figure, called a "nutation", causes an Earth orbital spirical oscillation, known as the famous Chandler "wobble". The equatorial bulge, the rotation axis' angle of inclination to the ecliptic plane, the gravitational tidal forces of the Sun, Moon and planets, have an affect on the Earths' orbit that produces the famous precession of the equinoxes.
Axial Tilt: the ecliptic is the plane of the Earth's ellipsoidal orbital path around the sun; the rotation axis is currently inclined to the ecliptic by an angle of 23.5 degrees: this is called the obliquity, or tilt, of the axis. It is this axial tilt that causes our annual seasons. Due to orbital dynamics, the obliquity varies between a minimum of 21 degs. 39 mins. and a maximum of 24 degs. 36 mins. over a 41,000 year cycle. The axial tilt's rate of change, (angular differentiation), is currently measured as .013 degs. per century.
Axis of maximum moment of inertia = the axis of figure: because the Earth is not a perfect sphere, but is physically an oblate spheroid, the position of the axis of figure is not a precise constant, but is affected by the constant change in the earth's distribution of total mass: (ie, by ocean tides, atmospheric conditions, plate tectonic movements, etc.).