‘以武會友’ means to make friends with martial arts.
As people share a meal they have prepared with others, friendships are formed through this shared experience and motion. Though a game or competition deciding the winner and loser is fun, the art of sharing and experiencing together is also profoundly enjoyable and valuable.
Everyone who practices martial arts is a friend and a colleague walking the same path. There may be a slight difference in the way people go about the road or in the way of walking, but we are all along the same path.