History and Theology for Christian Faith

"Christ died"—that is history; "Christ died for our sins"—that is doctrine. Without these two elements, joined in an absolutely indissoluble union, there is no Christianity.
  -- p23, J. Gresham Machen in Christianity and Liberalism

Church: the gathering, the display, and the means

Reformed theology has certainly realized that the church has two sides, and that besides being the assembly of believers and the revelation of the body of Christ, she must also be the means by which new believers are added.
  -- p263, Vos, Doctrine of the Covenant in Reformed Theology, from Redemptive History and Biblical Interpretation

Baptism and continuation of the church from generation to generation

For [a Reformed believer] that continuity is assured by the faithful promise of God. Hence, in back of Word and sacrament he places the covenant as the strongest expression of how the unbroken work of grace from generation to generation rests, as all grace, on the sovereign pleasure of God. The church does not abide because we baptize or work regeneration by baptism; rather because God establishes His covenant from generation to generation, therefore, the church remains and we baptize. Since it is God’s covenant and not man’s, it is appropriate for the Christian to recognize this goodness of God in quiet gratitude and in faith and to be strengthened by its sealing.  -- p261, Vos, Doctrine of the Covenant in Reformed Theology in Redemptive History and Biblical Interpretation 

Sacraments: particular signs to an all-comprehensive grace

In this connection it may also be noted that the idea of the covenant has prevented too narrow a view of the sacraments. Viewed as seals of the covenant, the sacraments possess just as universal and comprehensive significance as the covenant itself. They cease being signs of a particular grace and become what they should be: particular signs of an all-comprehensive grace. They seal Christ to us, the rich and full Christ, with all that we have in Him. We cannot limit that sealing power to any single stage of the way of salvation. Not regeneration, nor justification, nor the communion of the saints, each in itself, but all of these, as they together constitute the blessings of the covenant, are the object of sealing. If the consciousness of the covenant reflects like a mirror the glory of God, then all the separate rays come together in the sacraments, as a focal point, to one glory.
  -- Italics original, bold mine, p262, Vos, Doctrine of the Covenant in Reformed Theology in Redemptive History and Biblical Interpretation

Everything only through Jesus Christ

(Source: https://en.wikipedia.org/wiki/Geerhardus_Vos)

‘Only when the believer understands how he has to receive and has received everything from the Mediator and how God in no way whatever deals with him except through Christ, only then does a picture of the glorious work that God wrought through Christ emerge in his consciousness and the magnificent idea of grace begin to dominate and form in his life. For the Reformed, therefore, the entire ordo salutis [order of salvation], beginning with regeneration as its first stage, is bound to the mystical union with Christ. There is no gift that has not been earned by Him. Neither is there a gift that is not bestowed by Him and that does not elevate God’s glory through his bestowal. Now the basis for this order lies in none other than in the covenant of salvation with Christ. In this covenant those chosen by the Father are given to Christ. In it he became the guarantor so that they would be planted into His body in the thought-world of grace through faith. As the application of salvation by Christ and by Christ’s initiative is a fundamental principle of Reformed theology, this theology has correctly viewed this application as a covenantal requirement which fell to the Mediator and for the fulfilling of which He became the guarantor. In this way Reformed theology simply showed that here too it would be content with nothing but its one all-embracing slogan: the work of grace in the sinner as a mirror for the glory of God.’

  -- p248, Geerhardus Vos, The Doctrine of the Covenant in Reformed Theology in Redemptive Historyand Biblical Interpretation