A gate is a permanent portal between two dimensions.
Gates are typically openend (and closed) by seraphim angels with a special type of magic granted by their halos. Although rare, it's possible to make gates with other types of magic, but only seraphim can make a connection that goes through Heaven. Anyone or anything can pass through a gate freely.
Heaven has many permanent gates to points both in- and outside its seven circles. Although angels are able to teleport themselves between dimensions, the gates are needed to transport things too large to carry, or create clear passages to highly trafficked areas.