"I write unto you, fathers, because ye have known him that is from the beginning." (1 John 2:13)
Often this widely used term refers to ancestors, both as family lineage (our fathers) or as significant contributors from the past (founding fathers, church fathers). And occasionally to someone responsible for inventing or starting something important (father of modern medicine, father of our country). Sometimes it is used as a title of respect to a leader, a scholar, or a seasoned elder who has gained recognition for wisdom from long experience.
John emphasizes that latter sense in our text, refering to mature Christians who have been involved "from the beginning"--possibly referring directly to those like himself who have firsthand knowledge of the events of Christ's ministry. Such men would have "known him" (twice emphasized, 1 John 2:13 and 2:14) and should provide valuable strength and wisdom for the "children" and "young men" that need their counsel.
But this instruction goes beyond recognizing the contribution of first-generation Christians. Here the single most significant attribute of these fathers is that they have "known" the One "that is from the beginning," emphasizing the Greek idiom which denotes the unique attribute of the Source (eternal existence) of our relationship with God.
These fathers "know" this attribute, not merely as an intellectual concept or theological doctrine, but as the specific word choice demands, a knowledge that is grounded on personal experience. These fathers, having walked with the Lord for the many years of their lives, have passed the intellectual "knowledge" of the mind's eye, however clear and pure that sight may be, to confidence borne out by prayers answered, battles fought, and victories won. HMM III