The Bible often divides people into two classes, antithetically related. There are the sons of Cain and of Seth (Gen. 4-6), Israel and the nations (Ex. 19:5-6), the righteous and the wicked (Ps. 1), the wise and the foolish (Prov. 1:7), the saved and the lost (Matt. 18:11), the children of Abraham and those of the devil (John 8:39-44), the elect and the nonelect (Rom. 9), believers and unbelievers (1 Cor. 6:6), practitioners of the wisdom of the world and of the wisdom of God (1 Cor. 1-2), those who walk in light and those who walk in darkness (1 John 1:5-10), the church and the world (1 John 2:15-17).
These antitheses aren’t all equivalent. That is to say that they are not simply alternate names for the same two groups. The distinction between elect and nonelect, for example, is not the same as the distinction between believer and unbeliever. There are elect people among the current group of unbelievers, and that fact motivates missions and evangelism. So in Acts 18:10, the Lord assured Paul that “I have many in this city who are my people,” many elect who had not yet embraced the gospel.
Similarly under the Old Covenant, there were Gentiles like Melchizedek, Rahab and Ruth, who entered the people of God; and, as Paul says in Rom. 9:6, “not all who are descended from Israel belong to Israel.” Some Gentiles, then, belong to God’s people, and some Jews, in their hearts, do not. So the distinction between elect and nonelect is different from the distinction between Jew and Gentile, between Israel and the Nations.
Further, the antithesis between wise and foolish, for example, is a division within the body of professing believers. Nevertheless, wisdom and not foolishness is the mentality proper to believers in the Lord. Foolishness really belongs outside God’s people. In a believer, foolishness contradicts his belief in God. In the consummation glory, all believers will be wise, not foolish. The antithesis of belief/unbelief and elect/nonelect, is also a distinction destined for dissolution. In the end, all elect will be believers, just as, even now, all nonelect are unbelievers.
In that way, given these nuances and qualifications, the antitheses actually coalesce. There is a great big ugly ditch, to abuse the metaphor of Lessing, that runs through the human community. Some are on one side, some on the other. Although the location of that ditch is not always plain today, God will make it plain in his final judgment. Eventually the inconsistencies of believers and of unbelievers will be erased, everyone will show their true colors, and the antithesis will be fully manifest.