The most straightforward reason single predestination ought to be rejected is because it is unbiblical. The Bible repeatedly teaches that God predestines individuals to faith and salvation just as surely as he predestines non-elect individuals to condemnation, and that both of these decrees follow unconditionally from his will. Nevertheless, some false doctrines are more dangerous than others. While those who believe in single predestination are not outside the pale of orthodoxy, it is nevertheless still a very dangerous doctrine?
To be sure, those who affirm single predestination affirm absolute monergism without wavering as surely as any double predestinarian. What is the problem then? The problem is that they basically teach what amounts to an Arminian doctrine of reprobation. Teaching a Calvinistic view of salvation while teaching an Arminian doctrine of reprobation is obviously inconsistent. Indeed, nobody is perfectly consistent. However, it is terribly dangerous to be inconsistent on a doctrine so closely related with salvation.
The danger with theological inconsistency is that it produces theological instability. Humans crave consistency, and will oftentimes attempt to articulate doctrines in such a way as to make them consistent in their minds even in places where scripture does not offer such a luxury. To be sure, there are biblical doctrines that do not seem logically or theologically consistent as far as human thought is concerned. Obvious examples would be Christ’s hypostatic union or the doctrine of the Trinity. However, the Bible does provide us with a logically consistent theology when it comes to the relation of election and reprobation, and we would do well to follow it.
Where is the danger of instability in the doctrine of the relation of election to reprobation? Theologically, scripturally and logically, it is true that God predestines individuals to condemnation and that the ultimate ground of this is simply his sovereign will, rather than foreknowledge of the sinfulness of the reprobate. Nevertheless, the single predestinarian, like the Arminian, equates attributing the final cause of sin to God as making God morally culpable for sin.
This is unbiblical, and, frankly, Arminian. Paul’s point in Romans 9:19-23 is that God is righteous to predestine individuals to condemnation based solely on his will because he is a potter and we are the clay, and he has the right to do whatever he wants with us just as the potter has the right to do whatever he wants with his clay. In other words, Paul reasons that, for God to be the final cause of sin, does not mean that God is morally culpable for sin. To look at it from another perspective, the single predestinarian, like the Arminian, presupposes that culpability for sin presupposes the power of contrary choice. This is the complete opposite of Paul’s logic in Romans 9:19-23. God is the ultimate cause of personal sin and damnation, yet he is not culpable for sin because he is righteous in doing what he will with his clay as creator and sovereign potter.
For the single predestinarian, God has not predestined anyone to sin. Instead, man has free will with respect to salvation, but simply chooses not to because of their depravity. In other words, God is not sovereign over their reprobation. God is only sovereign over their salvation. It is impossible to have a Calvinistic doctrine of election alongside an Arminian concept of reprobation with any degree of stability. Such an individual borders on being a Calvinist and an Arminian at the same time, and this is a very frightening place for someone to be. Such an individual knows deep down that their doctrine makes absolutely no sense, and they will have a natural desire to experience the logical consistency in this area which God gladly provides, and which they refuse. The only way of resolving this unscriptural contradiction in their minds is to become an Arminian with respect to salvation or a Calvinist with respect to reprobation. Hopefully, this craving for consistency will lead them to become double predestinarians.