The earliest Rule was found in the Guarnacci Library in Volterra. This primitive document is known as the Earlier Exhortation, or the Earlier Version, of "The Letter to All the Faithful" and was likely composed before 1215. An expanded version, the Later Exhortation, was completed by about 1220. Both have been established as having been composed by Francis. Both documents call the lay faithful to a life of penance, i.e., of turning away from sin and toward God.
In the Earlier Exhortation, Francis describes the elements of the conversion process: 1) love God 2) love one's neighbor 3) turn away from our sinful tendencies 4) "receive the Body and Blood of our Lord Jesus Christ" and, as a result of the above, 5) producing worthy fruits of penance – a renewed life characterized by charity, forgiveness and compassion toward others.
Francis speaks in ecstatic terms of those who embrace this way of life: "Oh, how happy and blessed are these men and women when they do these things and persevere in doing them since the Spirit of the Lord will rest upon them and He will make His home and dwelling among them. They are children of the heavenly Father whose works they do, and they are spouses, brothers, and mothers of Our Lord Jesus Christ."
The "primitive rule" was approved by Pope Honorius III in 1221 with the Memoriale Propositi. Then, the rule was revised in 1289 by the Franciscan Pope Nicholas IV with the Supra Montem and by Pope Leo XIII approving in 1883 Misericors Dei Filius. The current rule was given by Pope Paul VI in 1978 with the Apostolic letter Seraphicus Patriarcha. It is designed to adapt the Secular Franciscan Order to the needs and expectations of the Church in the conditions of changing times.
The spirit of the Rule can be found in Article 4: "The rule and life of the Secular Franciscan is this: To observe the Gospel of our Lord Jesus Christ by following the example of St. Francis of Assisi, who made Christ the inspiration and the center of his life with God and people.'Christ, the gift of the Father’s love, is the way to him, the Truth into which the Holy Spirit leads us, and the life which he has come to give abundantly. Secular Franciscans should devote themselves especially to careful reading of the Gospel, going from Gospel to life and life to the Gospel."