That which was from the beginning, that which we have heard, that which we have seen with our eyes, that which we saw, and our hands touched, concerning the Word of life
The echoes of the great prologue in John's gospel are so pronounced in these first four verses, with just those variations which are believable in John but which no forger would have dared to attempt, that this shorter prologue here has been understood by the Christians of all ages as a convincing Johannine signature.  Nobody except John could have written this.