castaway, rejected, reprobate

“Epistolary Communications: The Castaway” From Concise Bible Dictionary:

1 CORINTHIANS. 9: 27.
COR 9: 27 Dear Brother-It is well known that this verse, especially this expression, has given rise to much difference of thought among intelligent believers; yet I cannot doubt that the remarks in the Bible Witness and Review, 1. 311, unduly soften what is meant to be a grave word for conscience. What led to the effort to tone down the passage (still prevalent among many saints and teachers) was the dread of enfeebling grace and undermining the everlasting security of the believer. For so men have insisted as to the text till our day from Chrysostom's. Εἱ φὲ Παῦτο δέδοιχεν ὁ τοσούτους διδάξας, χαὶ δέδοιχε μετὰ τὸ χηρῦξαι χαὶ γενέσθαι ἄγγελος χαὶ τῆς οἰχουμένης τὴν προστασίαν ἐπιδείξασθιαι, τὶ ἄν εἴποιμεν ἡμεῖς; Μὴ γὰρ δὴ νομίσητε, φηςὶν, ἐπειδὴ ἐπιστεύσατε ὅτι ἀρχεῖ τοῦτο εἰς σωτηρίαν ὑμῖν. Εἰ γὰρ ἐμοὶ τὸ χηρῦξαι, τὸ διδάξαι, τὸ μυρίους προσαγαγεῖν οὐχ ἀςχεῖ εἰς σωτηρίαν, ει μὴ χαὶ τὰ χατ’ ἐμαυτὸι παρασχοίμυν ἄληπτα, πολλῷ μᾶλλον
(Field's edit., ii. 273, Oxon. 1847). Language like this did not commend itself to one enjoying salvation by grace, as taught in Eph. 2 and Titus 3 Hence the disposition to run into the opposite extreme, as expressed in the note of the Bishops' Bible, and to regard ca6vItos as no more than "disapproved" by men, or, if by God, only as to the reward of service. So Calvin (Com. in 1.): " Nonnulli exponunt: Ne, quum alias bene ac fideliter docuero, male vivendo damnationis iudicium a Deo reportem. Sed melius quadrabit relatio huius verbi ad homines, hoc modo: Vita mea aliis regula quaedam esse debet. Contendo igitur ita me gerere, ne doctrinae mores mei et opera repugnent: atque ita cum magno meo dedecore et gravi fratrum meorum offendiculo
ea negligam que ab aliis requiro." (Comment. 1. 321, 322, ed. Tholuck.)
But I am persuaded (and have been ever since 1858) that this view is wrong. Therefore I regret the reproduction of the brief old note (which I should not have permitted had I noticed it when sent for revision in proof). It is a question of salvation, not of reward of labor, as in chap. iii., while in this context not to obtain an incorruptible crown is to be lost. As the verse in no way insinuates the Arminian fear of perdition for one born of God, so the Calvinistic interpretation, which sees no more than failure in service, is uncalled for and untenable. It seems plain that the apostle means, in the strictest and fullest way, a rejection of the person as worthless-not a mere condemnation of his ministry (indeed this is not discussed), but his own reprobation. Preaching to others is supposed, without impeaching either orthodoxy or zeal, but the man himself ἀδόχιμος. The fear of compromising grace in God, or the believer's security, is groundless; for it is no question of a believer but of a preacher, who may preach well enough but exercises no self-judgment or self-denial, who does not keep the body in subjection, and consequently goes on without conscience before God. It is an unrenewed man, who may preach ever so ably and acceptably, but is indifferent to holiness. What can become of him 2 Is he not reprobate? and "reprobate " is the genuine sense of the word here and everywhere in the New Testament, save in a passage of Hebrews (vi. 8), which applies to ground fruitless of all that is good, fruitful only of thorns and briars, whose end is to be burned. Surely this figurative use only strengthens the case.
The tendency to make preaching everything, to the neglect of holiness, was the snare laid for the Corinthians. In the eye of some it was plain that gift and work were all, the will of the Lord in a godly life of no account practically. Against it the trumpet here sounds the alarm.
Why, then, does the apostle speak of himself hypothetically rather than of those imperiled souls directly? Because he walked in the Spirit with the finest sense of delicate consideration. He preferred out of love to put it to his own case. Not, as too many imagine, that he had the least doubt or fear as to himself; not that a single text raises the smallest anxiety about any one possessing life in Christ. Yet whoever throws off vigilance and self-restraint, whoever lives contrary to Christ, may preach as well as you like, but he will certainly be lost, were it Paul himself. As he says in chapter iv. of this Epistle, he has transferred the application to himself, if not to Apollos. Thus it is purely hypothesis, while the fact was as far as possible from Paul; but he thus unsparingly applied it to himself, if he walked recklessly, for the warning of some in the Corinthian assembly. It is hardly so strong as Heb. 12:14,15, from which we must not be driven by abuse or by ignorance; nor should we blunt its edge in the warning given to lax professors of Christ. -Ever yours affectionately in Christ,

“Reprobate (Maas)” From Concise Bible Dictionary:

God’s ancient people in their condition of moral debasement are compared to “reprobate silver,” or “refuse silver” as in the margin (Jer. 6:30); or, as is read in Isaiah 1:22, “thy silver is become dross,” rejected.
In the New Testament the word is ἀδοκιμος, “disapproved,” and is applied to the wicked, and to those also who having engaged in the race fail to reach the goal (Rom. 1:28; 2 Cor. 13:5-7; 2 Tim. 3:8; Titus 1:16). The same word is translated “rejected,” and is descriptive of such as, in spite of gracious ministry, produce only that which is natural to fallen man (Heb. 6:8). It is also translated “castaway” in 1 Corinthians 9:27, where the apostle Paul represents himself as keeping under his body, and bringing it into subjection, lest having preached to others he himself should be rejected. This appears to indicate the possibility of a man, after having preached the gospel to others, being himself disapproved; failing to reach the goal through lack of self-discipline.
Photo of aluminum dross (left) and aluminum (right).

Strong’s Dictionary of Greek Words:

Greek:
ἀδόκιμος
Transliteration:
adokimos
Phonic:
ad-ok’-ee-mos
Meaning:
from 1 (as a negative particle) and 1384; unapproved, i.e. rejected; by implication, worthless (literally or morally)
KJV Usage:
castaway, rejected, reprobate