Having the peace of God is not enough

Question: "Suppose you have the peace of God. Will not that quiet you?"
Answer: "No, I must have the God of peace; as the peace of God, so the God of peace; that is, I must enjoy that God that gives me the peace; I must have the Cause as well as the effect; I must see from whence my peace comes and enjoy the Fountain of my peace, as well as the streams of my peace."
  -- Jeremiah Burroughs as quoted in Fred Sanders, The Triune God, p33–34

right doctrine but wrong spirit

'One of my own saddest recollections in pastoral ministry is of being told that during a new members' welcome that included a young husband with "a past," two "pillars of the church," esteemed for the model way in which they fulfilled all church membership responsibilities, were overheard to say, "What's he doing joining the church?" How easy it is to fall into a spirit of conditional grace toward prodigals even when the right doctrinal notes are struck!' - Sinclair Ferguson, The Whole Christ, p73fn35

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

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 

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

Do muslims and Christians worship the same God?

After some unfortunate events at Wheaton College, there have been a several online posts regarding the question whether muslims and Christians worship the same God. I haven't been following the events or the arguments too closely, but here's what Calvin said, around 500 years ago.

So today the Turks (that is, muslims), although they proclaim at the top of their lungs that the Creator of heaven and earth is God, still, while repudiating Christ, substitute an idol in place of the true God.
  -- Calvin, Institutes, II. vi. section 4