What are seraphim?

The seraphim (“fiery, burning ones”) are angelic beings associated with the prophet Isaiah’s vision of God in the temple (Isaiah 6:1–7). Isaiah describes the scene: “Above [the Lord] were seraphim, each with six wings: With two wings they covered their faces, with two they covered their feet, and with two they were flying.
At the sound of their voices the doorposts and thresholds shook and the temple was filled with smoke” (Isaiah 6:2–4). It would seem from this passage that seraphs are angels who worship God continually.

Isaiah chapter 6 is the only place in the Bible that specifically mentions the seraphim. Each seraph had six wings. They used two to fly, two to cover their feet—that is, the whole lower half of their bodies—and two to cover their faces (Isaiah 6:2). Nineteenth-century Scottish pastor Alexander MacLaren, in his Expositions of Holy Scripture, saw the three pairs of wings as carrying special significance:

The seraphim flew about the throne where God was seated, shouting His praises as they called special attention to God’s holiness, glory, and majesty. The voices of these beings were so powerful that the temple was shaken to its very foundation. These seraphim apparently also served as agents of purification for Isaiah as he began his prophetic ministry. One of them flew to the altar, took a hot coal, and placed it against Isaiah’s lips with the words, “See, this has touched your lips; your guilt is taken away and your sin atoned for” (Isaiah 6:7).

Along with the other types of holy angels, the seraphim are perfectly obedient to God.