It is common knowledge among monergistic Christians that it is totally unacceptable to add to Christ's justification. It is faith alone in Christ which justifies, and any addition to this compromises and nullifies the Gospel, making it of none effect. However, it is less often appreciated by many contemporary monergists how unacceptable it is to add even non-works based conditions to salvation. Contemporary monergists reject Arminianism, of course, but few seem to realize how serious a problem it is based on scripture. To believe in election according to God's foreknowledge of our faith, for example, is no less serious a problem for Paul than justification by works. This is clear from Romans 9:6-13 and v. 16:
6 But it is not as though the word of God has failed. For not all who are descended from Israel belong to Israel, 7 and not all are children of Abraham because they are his offspring, but “Through Isaac shall your offspring be named.” 8 This means that it is not the children of the flesh who are the children of God, but the children of the promise are counted as offspring. 9 For this is what the promise said: “About this time next year I will return, and Sarah shall have a son.” 10 And not only so, but also when Rebekah had conceived children by one man, our forefather Isaac, 11 though they were not yet born and had done nothing either good or bad—in order that God's purpose of election might continue, not because of works but because of him who calls— 12 she was told, “The older will serve the younger.” 13 As it is written, “Jacob I loved, but Esau I hated.”...It depends, therefore, not on human desire or exertion, but on God who has mercy.
We see here that every form of conditional salvation. It is not merely that justification by faith is held up against justification by faith + works, but unconditional salvation broadly construed, and extending beyond salvation, is affirmed, and any condition added to any form of salvation is emphatically rejected. This includes:
1) Any form of salvation that is conditional on works (Rom. 9:11)
2) Any form of salvation that is conditional upon any desire in man (Rom. 9:16)
3) Any form of salvation that places a condition such that there is something about the person that moves God to save such a person (Rom. 9:10). The fact that Paul begins v. 10 with "And not only so" is particularly significant, because the Judaizing or Pharisaic objector to vv. 7-9 might have replied that Isaac was chosen as the child of promise because Ishmael was disinherited by his ethnicity. He was not a racial "purebred," since his mother was Hagar. Such a belief was clearly common among the Jews of Paul's day. It is implied, for example, in Jesus' rebuke of Nicodemus (Jhn. 3:1-15, cf. Matt. 3:9, Lk. 3:8, Jhn. 8:33, 37, 39, 40). Indeed, as John Gill points out, such a belief is reflected in the Talmud: "Says R. Akiba (c), even the poor of Israel are to be considered as if they were , "noblemen", that are fallen from their substance, because they are the children of Abraham, Isaac, and Jacob..." Paul seeks to anticipate and repudiate this objection with the example of Jacob and Esau, who were conceived by Rebekah and "one man, our forefather Isaac." The election of Jacob and rejection of Esau was therefore not conditional on any characteristic whatsoever in Isaac.
Indeed, as Paul goes on to affirm in the next verse, it was not conditional on the moral excellence of Isaac any more than Esau's reprobation was conditional on his moral dereliction, or God's foreknowledge thereof in either case. This is the significance of Paul's point that Isaac's acceptance and Esau's rejection took place "although they were not yet born and had done nothing either good or evil." Not only was Isaac's election not conditional on any moral excellence in him, but Esau's reprobation was not conditional on God's antecedent consideration of Esau's demerit. This is quite different from what is commonly heard in Reformed circles in defenses of the sovereignty of God in salvation.
We typically hear that all are deserving of condemnation, and that God would be just in condemning everyone. This is true, so far as it goes, but it goes not go far enough because Paul goes a great deal further. The ultimate cause of not only election, but reprobation, is conditional not on either our merit or demerit, but is wholly and ultimately contingent upon God's arbitrary will and decree. The question for the Christian should be: should election according to God's knowledge be regarded as any more orthodox than such a belief? Should we not affirm without qualification that God's salvation is utterly unconditional, and insist that this be a central criteria of orthodoxy? What about those who claim to be Reformed yet believe in the doctrine of the age of accountability, which makes election conditional upon the time of one's death (a belief that was unheard of in the Reformed world until around the 19th century)?