John 10:10 The thief cometh not, but for to steal, and to kill, and to destroy: I am come that they might have life, and that they might have it more abundantly.
What do you think about when you hear abundant life? Mansions with pools, servants and a large estate? How about friends and family, lots and lots of children? How about fame, or power, or title?
I once thought along those lines until Christ gave me a more abundant life.
Ephesians 4:13 Till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ:
I have grown in Christ. I might not have yet come to the full measure of that which God wills in His design for me, but the abundant life isn’t things being delivered, it is in the living itself.
John 20:31 But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name.
Galatians 2:20 I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
1 John 5:11 And this is the record, that God hath given to us eternal life, and this life is in his Son.
Jesus will share His life with us as much as we will allow it. There is the abundance. If our will looks to seek things, those desires take up room in our hearts meant for Christ. If my thoughts are of Him rather than of my selfish desires, then it is easier to see how He works in me to provide this abundant life.
Eternal life is not only to do with duration, but quality, as you have so clearly stated. Even the lost will “exist” for ever, but ours is forever too, and what a contrast in quality!