Boyd’s Bible Dictionary:
(sanctified). In O. T., a pious Jew (Psa. 16:3). In N. T., a Christian believer (Rom. 1:7; 8:27; Heb. 6:10).
Concise Bible Dictionary:
Two words are employed in the Hebrew.
1. chasid, “pious toward God,” also translated “holy” and “godly.” The word occurs frequently in the Psalms, where God speaks of His saints (Psa. 31:23; Psa. 50:5; Psa. 116:15; Psa. 149:1,5,9; etc.).
2. qadosh, “consecrated, set apart, holy” (Deut. 33:3; Job 15:15; Psa. 16:3; Psa. 34:9; Psa. 89:5,7; Dan. 7:18-27; Dan. 8:13; Hos. 11:12; Zech. 14:5). Aaron is called “the saint of Jehovah” (Psa. 106:16).
In the New Testament the word used is ἅγιος, which means “holy one.” A saint is one set apart for God; he is such by calling—not “called to be a saint” (Rom. 1:7; 1 Cor. 1:2; compare Heb. 3:1). Saints are thus a distinct, recognized class of persons belonging to God—His saints (Acts 9:13; Col. 1:26; 1 Thess. 3:13; Jude 1:14). All Christians are embraced in this class, so that the apostle could speak of “all saints” (Eph. 1:15; Eph. 3:18; Col. 1:4; Philem. 1:5). Christians therefore need not shrink from acknowledging the designation by which God has been pleased to distinguish them, and should ever remember that there is a line of conduct that “becometh saints” (Rom. 16:2; Eph. 5:3). The word ἅγιος corresponds with the Hebrew qadosh. The word chasid corresponds more with ὅσιος, translated “holy” (1 Tim. 2:8; Titus 1:8; Heb. 7:26; Rev. 15:4); and “Holy One” (Acts 2:27; Acts 13:35).
As there were many saints on the earth in Old Testament times, so we read in the Revelation that there will be saints on the earth after the church has been taken to heaven. Ignorance of this has often led to a mistaken application of the prophecies to the church (Rev. 13:10; Rev. 14:12; Rev. 18:24; Rev. 20:9).
From Anstey’s Doctrinal Definitions:
A “saint” is a “set apart one” or a “sanctified one.” All who know the Lord Jesus Christ as their Saviour are sanctified (positionally), and thus are saints.
In the KJV, Romans 1:7 says, “Called to be saints,” but the words “to be” are italicized, indicating that they are not in the Greek text and have been added by the translators to aid the reading of the passage. Unfortunately, it changes the meaning and makes sainthood a goal to be attained at some time in the future. (This is a Roman Catholic error. They teach that if a person lives nobly for that system, after he leaves this world through death, he may be promoted to the special place of being a saint.) The text should simply read, "called saints." This means that a person becomes a saint by obeying the gospel call. It is not something we hope to be, but something that the Word of God says that we are by the grace of God. There is no Scripture that tells us to try to attain to sainthood, but there are Scriptures that tell us that all believers are saints, even while they are still living in this world. Nevertheless, some people think that it is a mark of humility to refuse to call themselves a saint now, but it is not pride or presumption to believe the Word of God. In fact, a believer who refuses to call himself a saint is really denying the truth of Scripture.
A “sinner” in Scripture is a person who is not saved. However, when a person is justified, he is cleared from every charge of sin by being brought into a new position before God, wherein God no longer sees him in the position of a sinner, but rather, as a saint. Therefore, for believers to speak of themselves as being poor sinners is beneath the dignity of their position before God. It really denies the truth of what we are as sons of God. In a sense, it demeans the work of Christ which has saved us and set us in that new place of favour as “sanctified in Christ Jesus” (1 Cor. 1:2). We are not saying that Christians shouldn't use the term "sinners" in connection with themselves, but that they should say that we were once sinners.
W. Kelly said, "Some people talk of 'a believing sinner,' or speak of the worship offered to God by 'poor sinners.' Many hymns indeed never bring the soul beyond this condition. But what is meant by 'sinner' in the Word of God is a soul altogether without peace, a soul which may perhaps feel its want of Christ, being quickened by the Spirit, but without the knowledge of redemption. It is not truthfulness to deny what saints are in the sight of God" (Lectures on the Epistle to the Galatians, p. 47).
Mr. Kelly also said, "There prevails among too many evangelical persons a mischievous habit of talking about 'saved sinners.' To my mind it is not only inexact but misleading and dangerous. Scripture knows no such thing as a 'saved sinner.' We may rejoice over a 'sinner saved' if we know the mercy of it in our souls; but if we license the phrase—a 'saved sinner,' the moral effect is, that, when and though saved, he is still free to sin....It is perfectly true that, when God begins to deal with a soul, He certainly begins with him as a sinner; but He never ends there. I am not aware of any part of the Word of God in which a believer, save perhaps in a transitional state, is ever referred to as a 'sinner.'....It is evident that to be a saint and sinner at the same time is simply a flat contradiction. In short, Holy Scripture does not sanction such a combination, and the sooner we get rid of such phrases, which deserve no better name than religious cant, the better for all parties" (Lectures Introductory to the New Testament," pp. 213-214).
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There is an exception to this in James 5:19-20. James calls a failing believer a "sinner," but not in the sense of a positional thing as Paul and Peter use the term. James is rather speaking of what characterizes a believer who persists in following a course of sin in his life.