Passage
that which we have seen and heard declare we to you, that ye also may have fellowship with us, and our fellowship <FI>is<Fi> with the Father, and with His Son Jesus Christ;
that which we have seen and heard declare we to you, that ye also may have fellowship with us, and our fellowship <FI>is<Fi> with the Father, and with His Son Jesus Christ;
1 John 1:1 That which was from the beginning, that which we have heard, that which we have seen with our eyes, that which we did behold, and our hands did handle, concerning the Word of the Life--
1 John 1:2 and the Life was manifested, and we have seen, and do testify, and declare to you the Life, the age-during, which was with the Father, and was manifested to us--
1 John 1:3 that which we have seen and heard declare we to you, that ye also may have fellowship with us, and our fellowship <FI>is<Fi> with the Father, and with His Son Jesus Christ;
1 John 1:4 and these things we write to you, that your joy may be full.
1 John 1:5 And this is the message that we have heard from Him, and announce to you, that God is light, and darkness in Him is not at all;
The verse centers on "seen", "heard", "declare", "fellowship", "father", "jesus", and "christ". It is saying that the verse draws attention to "seen" and "heard", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 2's "and the Life was manifested and we..." into verse 4's "and these things we write to you...", so "seen" and "heard" belong inside that flow. In 1 John context, the local focus is Christ, faith, and discipleship.
A plain takeaway is to answer the verse's own emphasis on "seen" and "heard" with trust shaped by these words, not by a vague optimism outside the passage.