Please read Alan Kurschner's excellent post; it is a powerful article under the title, "God Owes Us Nothing" - which, I believe, gives helpful insight to this post below.
Reprobation is the antithesis to election and necessarily follows from it. If God does not elect a person, He rejects him. If God decides not to convert a sinner into a saint, He decides to let him remain a sinner (1). If God decides not to work in a man to will and to do according to God's will, He decides to leave the man to will and to do according to his own will. When God effectually operates upon the human will, it is election. When God does not effectually operate upon the human will, it is reprobation. Election is the expression of divine mercy; reprobation of divine justice. Paul teaches this in Romans 11:22, "Behold the goodness and severity of God (divine compassion and divine justice) on them which fell severity; but toward you goodness."
Reprobation relates to regenerating grace, not common grace. It is an error to suppose that the reprobate are entirely destitute of grace. All mankind enjoys common grace. There are no elect or reprobate in this refernece. Every human being experiences some degree of the ordinary influences of the Spirit of God. St. Paul teaches that God strives with man universally. He convicts him of sin and urges him to repent of it and forsake it (Roms. 1:19-20; 2:3-4; Acts 17:24-31).
Reprobation comprises preterition and condemnation of damnation. Preterition is a sovereign act; condemnation is a judicial act. God passes by or omits an individual in the bestowment of regenerating grace because of His sovereign good pleasure (eudokia). The reason of condemnation is known: sin is the reason. The reason for preterition is unknown: it is not sin, because the elect are as sinful as the nonelect. In preterition, God’s action is permissive; inaction rather than action. In condemnation God’s action is efficient and positive.
Preterition is “letting things stand” as they are. To omit or pretermit is to leave or let alone. The idea is found in Luke 17:34, “The one shall be taken, the other shall be left…”
Preterition in the bestowment of regenerating grace is plainly taught in Scripture (Isaiah 6:9-10*; Matt. 11:25-26; 13:11; 22:14; Luke 17:34; John 10:26; 12:39; Acts 1:16; 2 Thess. 2:11-12; 2 Tim. 2:20; 1 Peter 2:8; Rom. 9:17-22; Jude 1:4).
*Isaiah 6:9-10 is quoted more in the N.T. than any other O.T. text (4x’s in the gospels; 1x in Acts; and 1x in Romans). He said, "Go, and tell this people: 'Keep on listening, but do not perceive; Keep on looking, but do not understand.' "Render the hearts of this people insensitive, their ears dull, and their eyes dim, otherwise they might see with their eyes, hear with their ears, understand with their hearts, and return and be healed."
Source: William G.T. Shedd - "Dogmatic Theology"-third edition;
1. I don't think Shedd is not implying here that Christians are not any longer sinners. He is using the term to describe nature (unregenerate, sinner; regenerate, saint.) Saints are still sinners (Prov. 24:9) saved by grace through faith in Jesus Christ (Eph. 4-6). Our old nature has been crucified with Christ (Gal. 2:20-21; 2 Cor. 5:17). Though we have been completely delivered from the penalty of sin (salvation), we have not been delivered from the presence of sin (glorification) nor entirely from the practice of sin (sanctification) (Titus 2:12) until we are home with the Lord (Roms. 8:29-31; Titus 2:13). None of us have arrived to the fulness of our sanctification in this life... (Eph. 5:23-27; Rom. 12:1-2).
We all still struggle with sin and its desires (Rom. 7:7-10). But, as new creations in Christ, a genuine Christian will not be given over to the constant "practice of sin" without any repentance or sting of conscience (Gal. 5:16ff). We will be convicted of wrong actions and desire to please the Lord by ultimately turning from those things which do not honor Him. This is a struggle that even Paul faced in his own life (Rom. 7:14-20). When we do sin, our hope is that we have an adovate with the Father, Jesus Christ the righteous who intercedes for us (1 John 2:1-2). We are still sinners, that by God's grace are now made saints--His brethren (Heb. 2:11). We are new creatures but incarcerated in unredeemed flesh (Rom. 8:23) and there is the battle each day that we face in our daily walk in the Lord (Col. 3:1-14). And there is "no condemnation for those who are in Christ Jesus the Lord" (Rom. 8:1). I hope this helps clarify the distinction of what Shedd is saying here.