God is eternal…without beginning and without end.
“Before the mountains were brought forth,
Or ever You had formed the earth and the world,
Even from everlasting to everlasting, You are God.” Psalm 90:2
Eternal live is essentially God’s Life.
“[God]…who alone has immortality, dwelling in unapproachable light, whom no man has seen or can see, to whom be honor and everlasting power. Amen.” 1 Tim. 6:16
Eternal Life is not restricted or defined by chronological time.
“‘Your father Abraham rejoiced to see My day, and he saw it and was glad.’Then the Jews said to Him, ‘You are not yet fifty years old, and have You seen Abraham?’ Jesus said to them, ‘Most assuredly, I say to you, before Abraham was, I AM.’” John 8:56-58
As God the Son, Christ is eternal
“But you, Bethlehem Ephrathah,
Though you are little among the thousands of Judah,
Yet out of you shall come forth to Me
The One to be Ruler in Israel,
Whose goings forth are from of old,
From everlasting.” Micah 5:2
Eternal life is received when a person is redeemed (born again).
“Most assuredly, I say to you, he who believes in Me has everlasting life.” John 6:47
Eternal Life is Christ’s Life.
“Jesus said to him, ‘I am the way, the truth, and the life. No one comes to the Father except through Me.'” John 14:6
“Jesus said to her, “I am the resurrection and the life. He who believes in Me, though he may die, he shall live. And whoever lives and believes in Me shall never die. Do you believe this?”” John 11:25,26
“And this is the testimony: that God has given us eternal life, and this life is in His Son. He who has the Son has life; he who does not have the Son of God does not have life. These things I have written to you who believe in the name of the Son of God, that you may know that you have eternal life…” 1 John 5:11-13
God has made provision for Christ’s life to be the believer’s life source experientially.
“For you died, and your life is hidden with Christ in God. When Christ who is our life appears, then you also will appear with Him in glory.” Col. 3:3,4
“as His divine power has given to us all things that pertain to life and godliness, through the knowledge of Him who called us by glory and virtue, by which have been given to us exceedingly great and precious promises, that through these you may be partakers of the divine nature,” 2 Peter 1:3,4
This spiritual union of the Christian life is symbolized in the Vine – branch relationship.
“I am the vine, you are the branches. He who abides in Me, and I in him, bears much fruit; for without Me you can do nothing.” John 15:5
– JBW (NKJV quotes)
This article in PDF: What is Eternal Life?