After the salutation, the writer declares that he would communicate to his brethren something of that which he had himself received
All hail, you sons and daughters, in the name of our Lord Jesus Christ, who loved us in peace.
Seeing that the divine fruits of righteousness abound among you, I rejoice exceedingly and above measure in your happy and honoured spirits, because you have with such effect received the engrafted spiritual gift. Wherefore also I inwardly rejoice the more, hoping to be saved, because I truly perceive in you the Spirit poured forth from the rich Lord of love. Your greatly desired appearance has thus filled me with astonishment over you. I am therefore pursuaded of this, and fully convinced in my own mind, that since I began to speak among you I understand many things, because the Lord has accompanied me in the way of righteousness. I am also on this account bound by the strictest obligation to love you above my own soul, because great are the faith and love dwelling in you, while you hope for the life which He has promised. Considering this, therefore, that if I should take the trouble to communicate to you some portion of what I have myself received, it will prove to me a sufficient reward that I minister to such spirits, I have hastened briefly to write unto you, in order that, along with your faith, you might have perfect knowledge. The doctrines of the Lord, then, are three: the hope of life, the beginning and the completion of it. For the Lord has made known to us by the prophets both the things which are past and present, giving us also the first-fruits of the knowledge of things to come, which things as we see accomplished, one by one, we ought with the greater richness of faith and elevation of spirit to draw near to Him with reverence. I then, not as your teacher, but as one of yourselves, will set forth a few things by which in present circumstances you may be rendered the more joyful.
Source: Epistle of Barnabas (New Advent)