Eternal life is here regarded as so certain in thought that it is described as already coming to pass (5:24). The actual realization of eternal life, however, is at the end of the age when it becomes a priceless possession and no longer a precious prospect. But, this blessed promise is dependent upon the disciple continuing to hear and believe God's word. According to the Greek words used here, hearing and believing on just one occasion is not enough. One must continue to hear and believe God's word if he intends to remain in a saved state and avoid judgment (i.e., condemnation; Rom. 8:1).
Please study the following verses as proof that we only possess eternal life in prospect now: Mark 10:28-30, Romans 2:4-7, Titus 1:2, and I John 2:25. In these passages, eternal life is spoken of as becoming a reality "in the age to come". It is referred to as a "hope" and a "promise". Quite obviously, one does not seek for something already in his possession, one does not hope for that which has already been received, and one does not cling to a promise already realized. Paul explicitly wrote that one does not hope for that which he has (Rom. 8:24). In order to avoid contradiction, John 5:24 (as well as I John 5:13) must be interpreted as having eternal life in prospect for the faithful.
It appears that Jesus continues talking about salvation and a spiritual resurrection in John 5:25-27. There is no record that Jesus had raised anyone from the dead physically at this point in His ministry. However, He said the hour "now is" when the dead would hear His voice, "and those who hear will live." In other words, those who listen to and obey Jesus would find spiritual life and freedom from slavery to sin (cf. Rom. 6:17,18). Jesus, because He is the Son of Man (cf. Dan. 7:13,14), has the authority from the Father to offer spiritual life to His followers and "execute judgment" on the unfaithful and disobedient.
Jesus' power and authority to give eternal life and execute judgment are impressive. Nevertheless, Jesus says - "Do not marvel at this" (John 5:28). He is merely preparing them for the final wonder He is about to speak of--something even more exceptional to marvel at from a human perspective--the literal resurrection of all mankind!
According to Jesus in 5:29, "The hour is coming in which all who are in the graves will hear His voice" and be raised from the dead--some to the resurrection of life and the rest to the resurrection of condemnation (cf. Dan. 12:2). Even today, that hour is still coming (cf. Matt. 24:36ff; I Thess. 5:1ff). We can learn from this verse that eventually everyone will hear Jesus' voice. However, our goal should be to hear it in this life (through the Scriptures) and obey Him (cf. John 5:25).
Those to whom Jesus spoke on this occasion were unbelievers in Him, though they claimed to believe in God. It was therefore necessary for Jesus to show that He acted, not independently of the heavenly Father, but in perfect harmony with Him (5:30). Jesus sought to accomplish the Father's will, and the Father testified of Him in many ways, as our Lord will explain in the following verses.