The Eye of God is a vast portal which leads from the Lower Heaven (Empyrean) to the High Heaven (Jannah). It is guarded by an enormous Ophanim known as Wepset, which only allows beings native to the High Heaven, or “Pure of Heart” (a largely biased judgement based on if Wepset likes you or not) to travel using this rift. It is the only form of travel between the Lower and High Heavens.
The Eye of God resembles an enormous, swirling, vortex of light. It is usually shielded on all sides by the wings of Wepset, who only furls his wings to allow the worthy to pass through.