The normal order in Greek grammar is subject, verb, and object. In this sentence John placed the object—a couple of parallel relative clauses that include prepositional phrases—right in front and the subject and the verb much later. The object then is “that which was from the beginning.”
1 That which was from the beginning, which we have heard, which we have seen with our eyes, which we looked upon and have touched with our hands, concerning the word of life