At a later stage in the service, during the blessing of the font, the same candle is plunged three times into the water with the words: Descendat in hanc plenitudinem fontis virtus Spiritus Sancti" (May the power of the Holy Spirit come down into the fulness of this fountain). From Holy Saturday until Ascension Day the paschal candle is left with its candlestick in the sanctuary, standing upon the Gospel side of the altar, and it is lighted during high Mass and solemn Vespers on Sundays. It is extinguished after the Gospel on Ascension Day and is then removed.
The results of recent research seem all to point to the necessity of assigning a very high antiquity to the paschal candle. Dom Germain Morin (Revue Bénédictine, Jan., 1891, and Sept., 1892) has successfully vindicated, against Mgr. Duchesne and others, the authenticity of the letter of St. Jerome to Presidius, deacon of Placentia (Migne, P.L., XXX, 188), in which the saint replies to a request that he would compose a, carmen cerei, in other words, a form of blessing like our "Exultet". Clearly this reference to a carmen cerei (poem of the candle) must presuppose the existence, in 384, of the candle itself which was to be blessed by the deacon with such a form, and the saint's reply makes it probable that the practice was neither of recent introduction nor peculiar to the church of Placentia. Again St. Augustine (City of God XV.22) mentions casually that he had composed a laus cerei in verse; and from specimens of similar compositions — all of them, however, bearing a close family resemblance to our "Exultet "-which are found in the works of Ennodius (Opusc., 14 and 81), it appears that there can be no sufficient ground for doubting the correctness of this statement. Moreover, Mgr. Mercati has now shown good reason for believing that the existing "Præconium paschale" of the Ambrosian Rite was composed in substance by St. Ambrose himself or else founded upon hymns of which he was the author (see "Studi e Testi", XII, 37-38). There is, therefore, no occasion to refuse to Pope Zosimus (c. 417) the credit of having conceded the use of the paschal candle to the suburbicarian churches of Rome, although the mention of this fact is only found in the second edition of the "Liber Pontificalis". Mgr. Duchesne urges that this institution has left no trace in the earliest purely Roman Ordines, such as the Einsiedeln Ordo and that of Saint-Amand; but these speak of two faculæ; (torches) which were carried to the font before the pope and were plunged into the water as is now done with the paschal candle. The question of size or number does not seem to be very vital. The earliest council which speaks upon the subject, viz., the Fourth of Toledo (A.D. 633, cap. ix), seems to couple together the blessing of the lucerna and cereus as of equal importance and seems also to connect them both symbolically with some sacramentum, i.e. mystery of baptismal illumination and with the Resurrection of Christ. And undoubtedly the paschal candle must have derived its origin from the splendours of the celebration of Easter Eve in the early Christian centuries. As pointed out in the article HOLY WEEK, our present morning service on Holy Saturday can be shown to represent by anticipation a service which in primitive times took place late in the evening; and which culminated in the blessing; of the font and the baptism of the catechumens, followed immediately by Mass shortly after midnight on Easter morning. Already in the time of Constantine we are told by Eusebius (De Vita Constantini, IV, xxii) that the emperor "transformed the night of the sacred vigil into the brilliancy of day, by lighting throughout the whole city pillars of wax (kerou kionas), while burning lamps illuminated every part, so that this mystic vigil was rendered brighter than the brightest daylight". Other Fathers, like St. Gregory Nazianzus and St. Gregory of Nyssa, also give vivid descriptions of the illumination of the Easter vigil. Further, it is certain, from evidence that stretches back as far as Tertullian and Justin Martyr, that upon this Easter eve the catechumens were baptized and that this ceremony of baptism was spoken of as photismos, i.e., illumination. Indeed, it seems highly probable that this is already referred to in Hebrews 10:22, where the words "being illuminated" seem to be used in the sense of being baptized (cf. St. Cyril of Jerusalem, Cat. i, n. 15). Whether consciously designed for that purpose or not, the paschal candle typified Jesus Christ, "the true light which enlighteneth every man that cometh into this world", surrounded by His illuminated, i.e. newly baptized disciples, each holding a smaller light. In the virgin wax a later symbolism recognized the most pure flesh which Christ derived from His blessed Mother, in the wick the human soul of Christ, and in the flame the divinity of the Second Person of the Blessed Trinity. Moreover, the five grains of incense set cross-wise in the candle recalled the sacred wounds retained in Christ's glorified body and the lighting of the candle with new fire itself served as a lively image of the resurrection.
Of the practice of medieval and later times regarding the paschal candle much might be said. We learn on the authority of Bede, speaking of the year 701, that it was usual in Rome to inscribe the date and other particulars of the calendar either upon the candle itself or on a parchment affixed to it. Further, in many Italian basilicas the paschal candlestick was a marble construction which was a permanent adjunct of the ambo or pulpit. Several of these still survive, as in San Lorenzo fuori della mura at Rome. Naturally the medieval tendency was to glorify the paschal candle by making it bigger and bigger. At Durham we are told of a magnificent erection with dragons and shields and seven branches, which was so big that it had to stand in the centre of the choir. The Sarum Processional of 1517 directs that the paschal candle, no doubt that of Salisbury cathedral, is to be thirty-six feet in height, while we learn from Machyn's diary that in 1558, under Queen Mary, three hundred weight of wax was used for the paschal candle of Westminster Abbey. In England these great candles, after they had been used for the last time in blessing the font on Whitsun Eve, were generally melted down and made into tapers to be used gratuitously at the funerals of the poor (see Wilkins, "Concilia", I, 571, and II, 298) At Rome the Agnus Deis were made out of the remains of the paschal candles, and Mgr. Duchesne seems to regard these consecrated discs of wax as likely to be even older than the paschal candle itself.
(Source: New Advent)