Jesus said that He came "that they may have life, and have it to the full" (John 10:10).
In order to understand what He meant with fullness of life, I believe we need to go back to the creation account in Genesis.
The creation of Man
When God created Man, He created him in his image so that Man would be like God (Gen. 1:26). Being made in God's image meant that Man was originally godly.
God also created Man to do the work He purposed for man - to be fruitful and look after His creation (Gen. 1:26-28; 2:15).
Man was also created to live in fellowship with God and to walk with Him in unhindered intimacy (Gen. 2:25; 3:8-10).
God therefore created Man to be like Him, to do His work and to live in fellowship with Him.
When Man disobeyed God, he became separated from God, causing him to no longer be like God, no longer walk in fellowship with God and no longer able to fulfill God's will for Man.
God's original plan and purpose for Man's life was interrupted. The fullness of life that God had breathed into Man to fulfill God's purpose for his existence was stolen, killed and destroyed by the enemy! Consequently Man became separated from God's life and could no longer fulfill God's original purpose for him.
God's solution was to restore mankind to divine life and God's purpose for Man by sending His Son. Jesus came to model fullness of life as well as to restore Man to fullness of life.
Jesus demonstrated a completely human life, filled with the life of God, the Holy Spirit. The Son of God laid aside His divine rights and self-sufficiency to demonstrate a human life in complete dependency on God (Phil. 2:6-8; Heb. 3:14; Acts 10:38). Jesus always emphasised His complete dependency upon the Father to demonstrate how His followers were to live their lives (John 5:19,20; 8:28; 12:49; 14:10,31; 1 John 2:6).
Jesus, therefore lived in fullness of life - a life joined to God that revealed God's nature in true holiness and godliness (John 14:9); a life that revealed unhindered fellowship with God (John 14:11) and a life that demonstrated the work of God (John 4:34).
As the last Adam, Christ not only came to demonstrate true humanity as God intended it but also paid the price to restore Man to God's life - fullness of life! What the enemy had stolen, killed and destroyed, Jesus returned, resurrected and rebuilt through His death, resurrection and complete victory over the enemy (Rom. 5:14; 1 Cor. 15:21,22, 45; Col. 2:9-15).
Through faith in Christ, the believer is no longer separated from God but is joined to Eternal Life - fullness of life (Eph. 4:18; 1 John 5:11,12,20). The believer is therefore given fullness of life in Christ (Eph. 1:3; 2:5; 2 Peter 1:3; 1 John 4:15).
Fullness of life
Those who are in Christ are called and empowered to live their lives in true godliness and holines as they reveal God's nature (Eph. 4:24; 1 Peter 1:15,16); live in unhindered fellowship with God (Eph. 2:18; 3:12; 1 John 1:3); and do the work of God in the power of the Holy Spirit (Eph. 2:10; John 14:12).
Those who are in Christ Jesus have been conformed to the image of God's Son so that they can live in fullness of life as God intended it for mankind (Rom. 8:29).
Glory to God for His indescribable Gift to us who believe and for fullness of life in Jesus Christ!