Beginning with the words of Christ: Fear not, little flock, because it has pleased your Father to bestow a kingdom on you (Lk 12:32), St Louis Marie applies these words to his Company of Mary. This short letter is an exhortation to the members of the Company to be faithful to their spirit of evangelical poverty and trust in the Providence of God. When it was written, it is probable that there were as yet no priests belonging to the Company, and St Louis Marie seems to foresee that the Congregation would always remain relatively small, since he insists on their not being discouraged on account of their small numbers. He insists, too, on hope and joy in the knowledge that God will care for them in his Providence.
The end of the manuscript is missing, finishing in the middle of a sentence, but an ending was supplied (probably by Fr Gabriel Deshayes) in 1837.
This Letter, together with the Burning Prayer for Missionaries and the Rule of the Missionaries of the Company of Mary, forms a triptych which has been accepted by the Holy See as part of the official Rule and Constitutions of the Company of Mary today, in the sense of their being the source of the modern Rule.