The covenant community (the visible church) is wider than the company of the elect (the invisible church). Put more eschatologically, the invisible church is the church as it will be fully revealed only on the last day. As in the Old Testament, the visible church or covenant com- munity is at present a “mixed body”: “Not all who are descended from Israel belong to Israel” (Rom. 9:6). There are weeds sown among the wheat (Matt. 13:36-43). In short, the visible church is the field in which the Father is at work, in the Son, and by his Spirit, producing a harvest for the end of the age. It is not simply the sum total of regenerate believers deciding and acting in concert, but the heavenly embassy on earth, where Christ is building his kingdom.
“The Church After Evangelicalism”, Michael Horton, in Renewing the Evangelical Mission, ed. Lints, 139.