“…the life was manifested, and we have seen, and bear witness, and declare to you that eternal life which was with the Father and was manifested to us…”
which was with the Father
Jesus in His eternity lived with the Father in eternity past. This is the preincarnate existence of the eternal Son. The Lord did not begin at Bethlehem or at the incarnation. He always existed eternally with the Father.
Jn 17: 5 “And now, O Father, glorify Me together with Yourself, with the glory which I had with You before the world was.”
and was manifested to us
Jesus “manifested” to the apostles is the incarnation. Jesus “was manifested” because He already existed. Jesus did not appear to the patriarchs and prophets as He appeared to the apostles. He appeared in the Old Testament in theophanes (physical manifestations of God) but He appeared to the apostles in person.
Jn 1: 14 “And the Word became flesh and dwelt among us, and we beheld His glory, the glory as of the only begotten of the Father, full of grace and truth.”
Co 3: 4 “When Christ who is our life appears, then you also will appear with Him in glory.”
We do not attain eternal life by our merit but we obtain it by the merit of Christ.
We cannot attain eternal life; we must obtain it. We cannot work for eternal life but we can obtain it as a gift. The Lord Jesus is that gift. There is no other way to go to the Father.
Jn 14: 6 “Jesus said to him, ‘I am the way, the truth, and the life. No one comes to the Father except through Me.’”
Ep 2: 8 “For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, 9 not of works, lest anyone should boast.”