Septuagesimatide
The Blessed Ildefonse Cardinal Schuster gives a little Septuagesima history in volume II of his Liber Sacramentorum. Herewith:
The Eastern usage regarded Saturday and Sunday as festival days, and therefore as exempt from the Lenten fast; so, in order to complete the forty days of Lent, the Greeks anticipated the penitential season by some weeks, and from this Sunday onward abstained from the use of meat. In the following week they abstained also from milk 'and similar foods, and finally on the Monday of Quinquagesima they commenced the rigid fast in preparation for Easter.
Among the Latins the custom varied at different times. By beginning the Lenten cycle with the First Sunday in Lent, there remain indeed, as St .Gregory remarks, forty days of preparation for Easter, but of these only thirty-six are devoted to fasting. In order to supply the four missing days, pious persons and ecclesiastics began, in quite early times, to abstain from meat on the Monday after Quinquagesima (In carnis privio or in carne levario = Carnival); but it is not until the time of St Gregory that we find in the antiphonary the liturgical consecration of the caput jejunii on the Wednesday of Quinquagesima.
The piety of the more devout, however, was not satisfied by these four supplementary days. The Greeks began earlier, and, living as they did beside them in Rome during the Byzantine period, the Latins could do no less. St Gregory therefore instituted, or at least gave definite form to, a cycle of three weeks' preparation for Lent, with three solemn stations at the patriarchal Basilicas of St Lawrence, St Paul, and St Peter, as though to begin the Easter fast under the auspices of the three great patrons of the Eternal City.
The order of the stational cycle has been reversed, and begins on this day with the station at St Lawrence, which holds the fourth place only among the papal basilicas, the reason for this change being that it was not considered advisable to remove the first Lenten station from the Lateran, where ever since the fourth century the Popes had been in the habit of offering the sacrificium quadragesimalis initii, as the Sacramentary calls it.
It would seem that the three Masses of Septuagesima, Sexagesima, and Quinquagesima date from the time of St Gregory, since they reflect the terror and grief that filled the minds of the Romans in those years during which war, pestilence, and earthquake threatened the utter destruction of the former mistress of the world.
The Introit is taken from Psalm xvii: "The groans of death surrounded me, the sorrows of hell encompassed me: and in my affliction, I called upon the Lord, and he heard my voice from his holy temple."
From this Sunday until Maundy Thursday the Gloria in Excelsis is omitted in Masses de tempore. Originally it was sung only at Christmas and Easter, but later it came to be used on all Sundays, except those in Lent, and also on the feasts of martyrs, but only by special privilege. The collect, which immediately follows the litany on days of fasting and penance, truly represents, therefore, the ordinary and normal form of the litany as used in the ancient liturgy of the Mass and of the divine office.
The collect betrays the deep affliction which weighed on the soul of St Gregory at the sight of the desolation of Rome and of all Italy during his pontificate. "O Lord, we beseech thee, graciously hear the prayers of thy people; that we who are justly afflicted for our sins may for the glory of thy name be mercifully delivered."
The Blessed Cardinal goes on to give some of the proper texts of the Mass and a bit of explanation of them. Most of that can be found in your missal. But there are a final couple of paragraphs on "the uncertainty of eternal salvation". These are worth posting, too:
How great is the uncertainty of eternal salvation! Cum metu et tremore vestram salutem operamini, as the Apostle says (Phil. ii I2); this is the fruit of to-day's meditation on the Epistle of St Paul and on the parable of the vineyard.
How many and how striking were the miracles worked by almighty God during the forty years that Israel wandered in the desert! The heavenly food, the miraculous water, the cloud and the column of fire, the Red Sea and the Jordan parting before them; and yet out of the many thousands for whom these wonders were worked, the greater number fell away, and only two reached the final goal.
Thus, it isn't enough for us to have been baptized, to have been called by God to a holy state, to the dignity of the priesthood, to have become the object of his special predilection by the frequent opportunities he has given us of receiving the holy sacraments and of hearing his gracious word. It is necessary to labour diligently -- operamini -- to follow the narrow way that leads to life eternal; it is necessary to imitate the chosen few -- that is the saints -- in order to be saved together with them. Never can we apprehend these divine truths with greater clearness than when we meditate upon them, as in today's station, beside the tombs of the martyrs, who, in order to gain their heavenly reward, were ready to sacrifice wealth, youth, and even life itself.