"In the terrible persecution that followed, the apostle John did much to confirm and strengthen the faith of the believers. He bore a testimony which his adversaries could not controvert and which helped his brethren to meet with courage and loyalty the trials that came upon them. When the faith of the Christians would seem to waver under the fierce opposition they were forced to meet, the old, tried servant of Jesus would repeat with power and eloquence the story of the crucified and risen Saviour. He steadfastly maintained his faith, and from his lips came ever the same glad message: “That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon, and our hands have handled, of the Word of life; ... that which we have seen and heard declare we unto you.” 1 John 1:1-3 . AA 568.2"
"That which we have seen and heard declare we unto you, that ye also may have fellowship with us: and truly our fellowship is with the Father, and with his Son Jesus Christ."
The EGW passage directly quotes 1 John 1:1-3, making it an explicit allusion rather than a thematic parallel. The confidence is raised to 1.00 because it is a direct quote.
"That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon, and our hands have handled, of the Word of life; (For the life was manifested, and we have seen it, and bear witness, and shew unto you that eternal life, which was with the Father, and was manifested unto us;) That which we have seen and heard declare we unto you, that ye also may have fellowship with us: and truly our fellowship is with the Father, and with his Son Jesus Christ."
Ellen White directly references 1 John 1:1-3 in this passage.