The heart of Reformed Christianity is its Trinitarian Christocentrism, expressed manwardly in evangelistic and pastoral proclamation attuned to human need, according to Christ’s Great Commission, and Godwardly in the worshipful offering, both corporately and individually, of responsive praise, prayer, thanksgiving, and song. Within this two-way street of communion with God and service of God, the sustained personal presence of the crucified, risen, reigning, and returning Lord with his people, and his constant personal address through Scripture heard, read, and preached, both to those who are his and to those who are not yet his, are integral and indeed central. Since the seventeenth century, the relational bond into which the Father through the Son draws sinners has been labeled the covenant of grace, and has been seen as undergirded by a prior plan and bond between the Father and the Son, which has been labeled the covenant of redemption. Both are witnessed to widely in Scripture, implicitly as well as explicitly, the fullest account of the covenant of grace (the new and eternal covenant) being found in the letter to the Hebrews, and the key evidence on the covenant of redemption (Christ’s mediatorial agenda, set by the Father) being contained in John’s Gospel. In this understanding of Christianity, Christ’s achievement by his cross of the corporate redemption of the whole church–past, present, and future–as the Holy Three know and love it, and thereby the individual redemption of everyone whom the Father has given to the Son to save, is both the mountaintop of glory, in the primary sense of God putting himself fully on display, and the wellspring of glory, in both the secondary sense of the spur to endless doxology and tertiary sense of divine action to glorify the redeemed in, with, and through Christ, so that they bear his image and likeness in a full sense.
J.I. Packer, From Heaven He Came and Sought Her