The short answer is that when the early Church converted pagans, it was felt that their earlier allegiances to pagan idols were, in fact, allegiances to demons. It was commonly held (correctly, I believe) by the Church fathers that the pagan gods were unclean and fallen spirits who tricked their followers into worship. They had to be cleansed of any spiritual contamination so a minor exorcism was included in the Baptismal rites. The old form of Baptism, which was changed at the time of Vatican II, included this as a 3-stage exorcism. It think it can still be used upon request of the parents (or an adult catachumen) and is a valid form of the rite. This was the old form of a Solemn Baptism in which I was baptized in 1958. (And thanks, Jerry Woznicki, my Godfather, who answered these questions in my place at St. Agnes! May the Lord bless and keep you in His arms!)
The old form included an initial exorcism that was done outside the church:
In the Exsufflation, after the initial questioning of the catechumen or sponsor, the priest then breathed 3 times on the candidate in the form of a Cross, recalling the Spirit (breath, wind, “ruach”) of God, and said:
Priest: Go forth from him (her), unclean spirit, and give place to the Holy Spirit, the Paraclete.
(Priest: Exi ab eo (ea), immunde spiritus, et da locum Spiritui Sancto Paraclito.)
Upon entry into the church:
Priest: I exorcise thee, unclean spirit, in the name of the Father + and of the Son, + and of the Holy + Spirit, that thou goest out and depart from this servant of God, N. For He commands Thee, accursed one, Who walked upon the sea, and stretched out His right hand to Peter about to sink. Therefore, accursed devil, acknowledge thy sentence, and give honor to the living and true God: give honor to Jesus Christ His Son, and to the Holy Spirit; and depart from this servant of God, N. because God and our Lord Jesus Christ hath vouchsafed to call him (her) to His holy grace and benediction and to the font of Baptism.
(Priest: Exorcizo te, immunde spiritus, in nomine Patris + et Filii + et Spiritus + Sancti, ut exeas, et recedas ab hoc famulo (hac famula) Dei N.: ipse enim tibi imperat, maledicte damnate, qui pedibus super mare ambulavit, et Petro mergenti dexteram porrexit. Ergo, maledicte diabole, recognosce sententiam tuam, et da honorem Deo vivo et vero, da honorem Iesu Christo Filio eius, et Spiritui Sancto, et recede ab hoc famulo (hac famula) Dei N, quia istum (-am) sibi Deus et Dominus noster Iesus Christus ad suam sanctam gratiam, et benedictionem, fontemque Baptismatis vocare dignatus est
Part III included a Solemn Exorcism that was performed in the Nave of the church:
Priest: I exorcise thee, every unclean spirit, in the name of God the Father + Almighty, in the name of Jesus + Christ, His Son, our Lord and Judge, and in the power of the Holy + Spirit, that thou be depart from this creature of God N, which our Lord hath deigned to call unto His holy temple, that it may be made the temple of the living God, and that the Holy Spirit may dwell therein. Through the same Christ our Lord, who shall come to judge the living and the dead, and the world by fire.
(Priest: Exorcizo te, omnis spiritus immunde, in nomine Dei + Patris omnipotentis, et in nomine Iesu + Christi Filii eius, Domini et Iudicis nostri, et in virtute Spiritus + Sancti, ut discedas ab hoc plasmate Dei N, quod Dominus noster ad templum sanctum suum vocare dignatus est, ut fiat templum Dei vivi, et Spiritus Sanctus habitet in eo. Per eundum Christum Dominum nostrum, qui venturus est iudicare vivos et mortuos, et saeculum per ignem.)
The priest would then take some spittle (re-enacting Mark 7:33-35) and touched the ears and nostrils of the Catechumen, which could be omitted for health reasons, and perform the Ephpheta:
Priest: Ephpheta, that is to say, Be opened, for an odour of sweetness. Be thou, devil, begone; for the judgement of God shall draw near.
(Priest: Ephpheta, quod est, Adaperire. In odorem suavitatis. Tu autem effugare, diabole; appropinquabit enim iudicium Dei.)
The Catechumen, or his/her sponsor if an infant, then formally renounced Satan:
Priest: N., do you renounce Satan? (Priest: N., abrenuntias Satanæ?)
Sponsor/Catechumen: I do renounce him. (Sponsor/Catechumen: Abrenuntio.)
Priest: And all of his works? (Priest: Et omnibus operibus eius?)
Sponsor/Catechumen: I do renounce him. (Sponsor/Catechumen: Abrenuntio.)
Priest: And all his pomps? (Priest: Et omnibus pompis eius?)
Sponsor/Catechumen: I do renounce him. (Sponsor/Catechumen: Abrenuntio.)
If someone was involved in a pagan or satanic religion before conversion, I would guess that the old form would be a good idea, but that would be something to discuss with one’s pastor.
The entire old form can be found here:
fisheaters.com/baptism2.html