Article 10 of the Statement of Faith states that unbelievers will experience "eternal conscious punishment." Why use the word "conscious"?

What we affirm of this biblical truth and why we do so is grounded in the Bible. We believe this statement because we believe it is taught in the Bible, which we have attempted to capture in our doctrinal statement in Article 10, Response and Eternal Destiny.

This phrase, "eternal conscious punishment," occurs in the longer statement that addresses the eternal destiny of believers and unbelievers. The complete statement is important to include in order to give this phrase its proper context: "We believe that God will raise the dead bodily and judge the world, assigning the unbeliever to condemnation and eternal conscious punishment and the believer to eternal blessedness and joy with the Lord in the new heaven and the new earth, to the praise of His glorious grace. Amen."

What we note in this statement, which reflects Jesus' statement in Matthew 25, is that there is an opposite symmetry between the eternal states of the only two groups of people that exist: unbelievers and believers. For unbelievers, those who have not responded to the gospel of Jesus Christ, they will be condemned and experience "eternal conscious punishment." For believers, those who have believed and received the gospel of Jesus Christ, they will experience "eternal blessedness and joy with the Lord." Both states are eternal; both states are conscious. And ultimately, this bodily resurrection and judgement of all will be "to the praise of His glorious grace."

The meaning of the specific phrase is expounded in Evangelical Convictions: An Exposition of the Statement of Faith of the Evangelical Free Church of America, 249-250:

Some, especially in recent years, have taken this language of death and destruction in a more literal sense and have argued that though God’s punishment of the wicked is real, it is not eternal. This view, known as “annihilationism” (or “conditional immortality”), holds that the unrighteous will cease to exist after they are judged. In this sense, the punishment for sin is eternal in its effect (that is, it is irreversible), but not eternal in the experience of the one judged. Our Statement denies such a view, contending that the Scripture teaches the continuing existence of persons—both believers and unbelievers—after the judgment, and that the experience of hell is eternal. Hence, we include the expression “eternal conscious punishment.”

Though the term “conscious” is not commonly used in historic confessions, what it expresses has been the almost universal view of the church through history, with, until very recently, only a few theologians and smaller sects standing in opposition. The church has held that the language of Scripture assumes that the destinies of believers and unbelievers, though very different, stand in parallel, and both will continue to experience the consequences of their choice through eternity.

Jesus himself established this connection when he spoke of the Son of Man separating two classes of human beings on the day of judgment as sheep and goats and saying to the goats on his left hand, “Depart from me, you who are cursed, into the eternal fire prepared for the devil and his angels… Then they will go away to eternal punishment, but the righteous to eternal life” (Matt. 25:41,46). It is true that the word translated “eternal” here (aiōnios) means “pertaining to the age to come.” But it is precisely because the age to come was perceived to be without end that the word is most commonly translated in this way. Because this verse uses precisely the same word to describe both the blessedness of the righteous and the punishment of the wicked, we must affirm that both enter into an unending conscious state.