The word amēn in Greek is taken directly from older, ancient languages such as Aramaic. It survives in many modern languages as well. Here, it is often given a fairly literal translation of “truly,” or something similar. Using this word at the end of a sentence is a way of emphasizing truth, or hopefulness. This is why we often end prayers with the word “Amen.” Used at the beginning of a statement, however, it means something very different. In that culture, Jesus’ use of “Amēn, amēn, legō hymin…”—”truly, truly I say to you”—means He is claiming absolute, first-hand, personal knowledge. This is not something He has learned or been taught. Rather, this is a fact He knows personally to be true.
This verse goes hand-in-hand with the statement made by Jesus in verse 23. Those who accept Christ are accepting God, and that means accepting eternal life. Rejecting Jesus means rejecting God. Those who reject God are under His judgment (John 3:36).
Jesus’ power over spiritual life and death is proven, in part, by His power over physical life and death (John 20:30–31).
The words Jesus uses place this eternal life in this moment—in the present. That is, those who put trusting faith in Christ have eternal life, right now. Their passing from “death to life” has already happened. This description of passing from death to life is only used in the New Testament by John, and only in two places. One is here, and the other is in 1 John 3:14.
Grace is a gift from our Heavenly Father given through His Son, Jesus Christ. The word grace, as used in the scriptures, refers primarily to enabling power and spiritual healing offered through the mercy and love of Jesus Christ.