Seized: this verb is better translated “overcame” (New Jerusalem Bible), “subdued” (Biblia Dios Habla Hoy), “overpowered,” or “captured.” It’s not that the angel just grabbed him, but that he overpowered him.

The dragon, that ancient serpent, who is the Devil and Satan: see 12.9.

Bound him for a thousand years, and threw him into the pit: the reader should not understand the text to say that the angel tied the Devil up with the chain for a thousand years and then threw him into the abyss. What is meant, of course, is that the angel overcame the Devil, bound him with the chain, and threw him into the abyss, where he stayed, bound, for a thousand years.

The pit: this is the abyss (see 9.1 and verse 1, above).

Shut it and sealed it over him: this assumes that there is an entrance, a door, to the pit, and it may be necessary for a translation to say so explicitly. With the key that he was carrying, the angel locked the door and then sealed it. So instead of translating shut (the door), as Revised Standard Version does, it is better to say “locked (the door),” as Good News Translation does. As in Matt 27.66, the sealing would be the use of some device to show that the door was not to be opened. The seal shows that the pit has been closed by God’s command. For seal one may also say “put a device on the door to make sure it stayed closed.”

He should deceive the nations no more: see in 12.9 “the deceiver of the whole world.”

Were ended: the same verb that is used in 15.1, 8.

He must be loosed: this is part of God’s plan, as the verb translated must shows (see 1.1). The Devil must be set free for a short period of time before his destruction. It is probable that the one who frees Satan is the angel who tied him up in the pit, so in languages that do not use the passive, one may say “After that, the angel will set him free for a short time.” However, if translators feel that the subject here is ambiguous, one may say “After that, they will set….”

Alternative translation models for verses 2-3 are:

• The angel overpowered the dragon, that ancient serpent also known as the Devil, or Satan, and bound him with the chain. Then he threw him into the abyss, and locked and sealed the door of the abyss. The Devil must stay there for a thousand years, and during that time he will not be able to deceive the nations of the world. After the one thousand years are over, he must be set loose for a little while.

Or:

• The angel captured the dragon, that serpent (or, snake) from ancient times whom they also call the Devil or Satan. He took the chain and tied the Devil up. Then he threw him into the deep pit. With the key that he was holding he locked the door of the pit and sealed it. The Devil must stay there for a thousand years, and during that time he will not be able to deceive the people on the earth. After the one thousand years are over, the angel will free him for a short time.

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on The Revelation to John. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .