The inspired Apostle wrote, “Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates?” (2 Cor. 13:5). How does a new convert examine himself truthfully having not been taught in the word and doctrine (Eph. 4:11-15; Rom. 16:17; 1 Tim. 4:1, 16, etc.)? As previously stated, the answer is the catechumen as seen in the Book of Galatians (6:1-6). In Scripture this interviewing is done. John did his interviewing – out loud at times. How did he know who to baptize and whom not to baptize? How did he know whom to call a viper and whom not to call a viper?

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Luke 7:7 He said therefore to the multitudes that went out to be baptized of him, Ye offspring of vipers, who warned you to flee from the wrath to come? Bring forth therefore fruits worthy of repentance, and begin not to say within yourselves, We have Abraham to our father: for I say unto you, that God is able of these stones to raise up children unto Abraham. And even now the axe also lieth at the root of the trees: every tree therefore that bringeth not forth good fruit is hewn down, and cast into the fire. And the multitudes asked him, saying, What then must we do? And he answered and said unto them, He that hath two coats, let him impart to him that hath none; and he that hath food, let him do likewise. And there came also publicans to be baptized, and they said unto him, Teacher, what must we do? And he said unto them, Extort no more than that which is appointed you. And soldiers also asked him, saying, And we, what must we do? And he said unto them, Extort from no man by violence, neither accuse any one wrongfully; and be content with your wages.
John apparently looked for a changed heart and evidence of the fruit. In John's exhortation to his hearers he articulates rather specific examples of repentance consistent with the sins of the categories of groups in question. Repentance should be discernible or evidenced in some way. Of course, in the Ethiopian eunuch’s case “the angel of the Lord” told Philip his mission (Acts 8:26) and the Spirit said to join himself to the Ethiopian’s chariot (29). Thus, no wonder this is a slam sprinkle baptism confirmed by the fact – “the Spirit of the Lord caught away Philip” (39) thereafter. Of course, we have Paul (Acts 19:1-5) asking the folks in Ephesus "what baptism did you receive." Of course, here we have Paul who wrote the book on discerning of spirits and Philip who had direct revelation from the “angel of the Lord” [i.e. a theophany of Christ] and the direct leading of the Holy Spirit. Now, JoeK I do not think either of us measures up to the likes of a Paul or Philip, do you? While we may having the gift of “the discerning of spirits” at times I see God utilizing secondary causes [examinations] to allow us to properly discern as well.

On a side note, Packer in Puritan Evangelism makes some interesting positive comments regarding Puritan “preparation”practices saying,

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It is never man, but always God, who determines when an elect sinner shall believe. In the manner of conversion too, God is sovereign. The Puritans taught that, as a general rule, conviction of sin, induced by, the preaching of the Law, must precede faith, since no man will or can come to Christ to be saved from sin till he knows what sins he needs saving from. It is a distinctive feature of the Puritan doctrine of conversion that this point, the need for “preparation” for faith, is so stressed. Man’s first step toward conversion must be some knowledge, of God, of himself, of his duty and of his sin. The second step is conviction, both of sinfulness and of particular sins; and the wise minister, dealing with enquirers at this stage, will try to deepen conviction and make it specific, since true and sound conviction of sin is always to a greater or less degree particularised. This leads to contrition (sorrow for and hatred of sin), which begins to burn the love of sinning out of the heart and leads to real, though as yet ineffective, attempts to break off the practice of sin in the life. Meanwhile, the wise minister, seeing that the fallow ground is now ploughed up, urges the sinner to turn to Christ. This is the right advice to give to a man who has shown that with all his heart he desires to be saved from sin; for when a man wants to be saved from sin, then it is possible for him genuinely and sincerely to receive the One who presents Himself to man as the Saviour from sin. But it is not possible otherwise; and therefore the Puritans over and over again beg ministers not to short-circuit the essential preparatory process. They must not give false encouragement to those in whom the Law has not yet done its work. It is the worst advice possible to tell a man to stop worrying about his sins and trust Christ at once if he does not yet know his sins and does not yet desire to leave them. That is the way to encourage false peace and false hopes, and to produce “gospel- hypocrites.” Throughout the whole process of preparation, from the first awakening of concern to the ultimate dawning of faith, however, the sovereignty of God must be recognized. God converts no adult without preparing him; but “God breaketh not all men’s hearts alike” (Baxter). Some conversions, as Goodwin said, are sudden; the preparation is done in a moment. Some are long-drawn-out affairs; years may pass before the seeker finds Christ and peace, as in Bunyan’s case. Sometimes great sinners experience “great meltings” (Giles Firmin) at the outset of the work of grace, while upright persons spend long periods in agonies of guilt and terror. No rule can be given as to how long, or how intensely, God will flay each sinner with the lash of conviction. Thus the work of effectual calling proceeds as fast, or as slow, as God wills; and the minister’s part is that of the midwife, whose task it is to see what is happening and give appropriate help at each stage, but who cannot foretell, let alone fix, how rapid the process of birth will be.

Reformed and Always Reforming,