The angels of the first sphere could be likened to the executive management of a corporation—they are responsible for directly interpreting the will of the CEO—God—and implementing it on the grandest scale.
These first-Sphere angels are the direct servants of God in heaven. The greatest of these are the Seraphim, which literally translated, means “burning ones”. These angels “burn” with the most intense love for God out of all the angelic beings, and are the closest to the throne of God, continuously shouting praises to the Lord and calling attention to His majesty and glory, ever-communicating this glory down through the ranks of the lower angels.
These angels are described in Isaiah 6:1-8 as having six-wings, with two covering their faces, two covering their feet, and two being used to fly. They are fiery in appearance, and the voice of even a single Seraph can shake the foundations of a building and fill it with smoke. It was a Seraph which touched a burning coal to the lips of Isaiah, purifying him in order that he might be able to prophesy.
If the Choirs of angels are thought of a gradient of holiness from most holy and just beneath God, to less holy, the Seraphim are nearer to God than any created being in the universe.
Interestingly, it is thought that Satan—once the highest of angels—was once a Seraph, his glory, light, and praise outshining that of all the other angelic beings. That light, however, turned to equivalent darkness when he betrayed God, and was cast from heaven.