Barth deals with the Canons [of Dordt] in his doctrine of election . During the discussion he refers several times to them. Right at the beginning he praises them for the fact that, in spite of the inclusion of reprobation in their doctrine of predestination, they formulated election itself in such a way that it really had "the character of evangelical proclamation."  This is particularly true of the formulation of Canons I,7.
Yet Barth has a very serious objection against their doctrine. He believes that in the Canons we find of a decretum absolutum, just as in the theology of all the reformers. Although they all maintained that our election is an "election in Christ" and spoke of Christ as the speculum electionis (Calvin)  or the liber vitae (Formula of Concord),  yet this "in Christ" was not the final word. Actually it referred only to the ordo salutis (Christ as the mediator and executor of our salvation). Behind this "in Christ" there was still deeper ground of election and reprobation: God's eternal decree, by which, in sovereign freedom, he decreed to save some in and through Christ and to leave others in their sin and perdition. The Arminians saw this serious defect, and over against the Calvinists they stated that "Christ, the mediator, is not only the executor of the election, but the foundation of the very decree of election."  Unfortunately their own understanding of the election was very faulty. ... Over against them the Calvinists of Dordt were altogether right, when they maintained that our salvation is wholly a matter of divine election. Unfortunately they maintained this by taking recourse to the decretum absolutum idea. In this same connection Barth criticizes Canons I, 7 , which before he had praised so highly.  Although Jesus Christ is mentioned, he is mentioned after the decision about election and reprobation has already been taken.
In all this we touch upon the very nerve of Barth's criticism. Again and again he returns to this point. ... Although at this point the Synod "almost exclusively" referred to "Jesus Christ, the Word of God and his promises," yet the doctrine could not work properly, as appeared rather soon after the Synod, because the decretum absolutum remained the last background. ...
Yet it cannot be denied that in the Canons this central aspect of the biblical doctrine of election [election is in Christ] does not receive the emphasis it deserves. Because [Canons of Dordt] I,7 is preceded by an article that speaks of a general double decree of election and reprobation, in which the "in Christ" aspect is altogether missing, the conclusion that there is a decretum absolutum behind the election-in-Christ could be drawn, ...
[Klaas Runia, Recent Reformed Criticisms of the Canons, in Peter Y. De Jong (ed.), Crisis in the Reformed Churches: Essays in Commemoration of the Great Synod of Dordt 1618-1619 (Grandville, MI, USA: Reformed Fellowship, 1968, 2008), pp. 196-197, 199]
 Karl Barth, Church Dogmatics, II, 2 p. 3-506
 Op. cit., 17/18.
 Calvin, Institutes, III, xxiv, 5
 Formula of Concord, Ep. XI, 7.
 C.D., II, 2, 67
 Op. cit., 69
In this interesting analysis of some critiques of the Canons of Dordt from those professing themselves to be Reformed, the late Klaas Runia in one section of his chapter interacted with the criticism that the Neo-Orthodox Karl Barth aimed against the Canons of Dordt. Runia's response to the Neo-Orthodox is to say that Dordt itself taught that election was done in Christ; that "the "in Christ" qualifies the act of choosing" (p. 198). Runia similarly opposes the idea of a decretum absolutum "behind the election-in-Christ" as being part of "later deterministic misunderstandings" which "have plagued and still are plaguing large sections of the Reformed community" (p. 199).
What are we to make of Barth's criticism of the Reformed doctrine of election as being voluntaristic, being build upon the foundation of decretum absolutum instead of in Christ (εν χριστω)? Is Runia's response to Barth a good one? While certainly the fact that Dordt does understand Christ to be the foundation of election is correct, is Runia correct in attacking the idea of a decretum absolutum "behind the election in Christ" as being part of "deterministic misunderstandings" plaguing the Reformed community?
To answer this, we must come to understand what the decretum absolutum concept means. How does God relate to His decrees? The manner in which Barth attacks the notion of God's decree seems to make them ontologically independent of God. However, is that really correct?
The decretum absolutum (Absolute or eternal decree), is the eternal decree of God in which He determines all that will happen. If God is sovereign at all, then the decretum absolutum must exist. The objection raised by Runia however it seems is whether this decretum is the foundation of election, assuming that Runia has no problem with the decretum existing in some sense.
The objection to making the decretum absolutum the foundation of election is that by so doing, the foundation is said to be no more on Christ. However, is that the case? What exactly does it mean for our foundation to be "in Christ"?
The first error in such an objection is a divorce or separation of the person and his thoughts, or in this case God and His thoughts. The thoughts (and decrees) of God precede from God and are distinct from Him. Ontologically therefore, God precedes His thoughts. However, as our God is the reasoning God, the Logos (cf Jn. 1:1-14), God cannot exist without His thoughts; neither can God's thoughts exist without Him. God and His decrees therefore can be distinguished, but they should never be separated.
In this light, to say that the foundation of an action (election) is based upon God's decrees (the decretum absolutum) is merely to say that the reason why God did an action is because He chose to do so. God chooses, but it is also a fact that it IS GOD who chooses. To say that the foundation of election is God's decrees is merely to say that it is in God, from whence these decrees originate.
The second error of such an objection is a confusion regarding the Trinity. The Trinity is one God in three persons, and the Christian God is always triune. Christians do not believe in a generic 'God' but only the triune God. The three persons of the Trinity are different in their roles (economically) and their "being" (the Son eternally begotten, the Spirit eternally proceeding). Yet, they are one God, not three Gods. The idea of a decretum absolutum talks about God's decrees, and therefore this refers to the triune God as a whole, undifferentiated. Therefore, it is in a sense God the Father's decrees as well as God the Son's decrees as well as God the Spirit's decree, though since it is not said of any particular person of the Godhead we should just humbly accept that it is true of the Godhead and each person as part of the Godhead, and not try to peak further into things which God has not revealed to us.
What this means is that it is not wrong to say that the foundation of election is in Christ and the foundation of election is in God, and from there go on to the idea of the decretum absolutum. To say that the foundation of election is God's will is to say that it is because of God, and therefore such is inclusive of Christ.
There is of course a special sense in which Christ is said to be the foundation of election as stated in Eph. 1:4. This is a federal union with Christ founded upon the eternal Covenant of Redemption the God the Father made with God the Son in eternity. However, this aspect of Covenant Theology is distinct from the idea of the decretum absolutum previously discussed, and the two must not be confused. The decretum is the epistemic foundation, while the Covenant motif refers to the working out of God's will in eternity and then in time. The former answers the 'why', the latter 'how'.
There is thus no error in saying that the foundation of election is the decretum absolutum. It is perhaps the case that Runia did not distinguish between the 'why' (epistemic) and 'how' (ontological) that discussion on the issue has been muddied. Barthians and their allies on this topic often accuse the decretum as making God voluntaristic. However, why that is a problem has never been proven conclusively. Is it because we do not LIKE the idea that God is God and His decisions are not subject to our vetting and approbation? As Paul replied to his imaginery objector on the same topic of election:
But who are you, O man, to answer back to God? Will what is molded say to its molder, “Why have you made me like this?” Has the potter no right over the clay, to make out of the same lump one vessel for honorable use and another for dishonorable use? (Rom. 9:20-21)
God is sovereign and free, and He is answerable to no one (In fact, all of us are answerable to Him!). The Barthians and their allies might not like and thus reject the answer given by Paul and Scripture, but they do not have the right to claim that Scriptures has not weighed in on this topic at all. Similarly, they can claim that they reject the non-separation of a person's thoughts and his person, but to continue on as if nobody has challenged their faulty ontology is a serious error on their part. In point of fact, it would be interesting to see anyone attempt to prove either Hegelian Idealism or Kantian Transcendental Idealism (the radical separation of the noumenal — das Ding an Sich — and the phenomenal), essentially any form of Idealism, from Scripture.