Kamphuis laments the dichotomizing of the covenant and the sacraments that Kuyperian scholasticism had produced by 1942:
That which applies to all the children is an external matter. It is, says the Praeadvies, “being children externally only” , and the Toelichting speaks about having a place within the Covenant and congregation of God “externally.” “Being children only externally” stands over against “being children unto salvation” , and belongs to the “external side” of the Covenant, according to the Praeadvies, which in this way intends to create a certain counterbalance against the continuing subjectivistic line.
However, here we encounter a distinction that will soon appear to be fatal, the distinction between “internal” and “external” in its application to the Covenant and the Word of God, the gospel of grace…
Once could either praise this strength and consistency or shudder because of these theological liberties. But we really have to deal with the facts here! Within the frame-work of this construction the sacraments are on the one hand undoubtedly seals of the general and conditional promise of salvation, but on the other hand they are no less than seals of the unconditional promise and proclamation of salvation. And this is, according to the Praeadvies, “the substance of the sacraments” the real kernel.
This way of thinking: “on the one hand” and “on the other” later led to the strange construction- covered even by John Calvin’s banner!- of two kinds of “integritas” (truthfulness and validity) of the sacraments. “Integer” apparently can have a false bottom- with God!
We are of the opinion that this is- and now we select the proper word with care- a horrible doctrine, and we find it hard to imagine that Christians could come to this. We can explain it as soon as we learn to see how great the power is of an un-Scriptural construction, which also has the power over the thoughts of people who are sincerely of the opinion that they are standing firm for the truth.
~ J. Kamphuis An Everlasting Covenant pg. 44-46