(3) And this is eternal life, that they may know You, the only true God, and Jesus Christ whom You have sent.
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This is the Bible's definition of eternal life: "to know God." We understand that "know," biblically, has a sexual connotation, implying experiential knowledge, not theoretical knowledge.
In Amos 5:4, God, through the prophet Amos, says, "Seek Me, and live!" He implies living eternally; if we seek God, we will have eternal life. Eternal life, however, does not especially have to do with time or duration because living the kind of life that God wants us to live is an enjoyable life, an abundant life. Just because a person lives eternally does not mean that he will be enjoying life. Consider the demons: They are not enjoying an abundant life though they live very long lives.
The Greek word aionios, translated here as "eternal," has to do with quality. Eternal life is the excellent, supreme life that God lives. When Jesus says that eternal life is to know God, He primarily implies a quality of life, and length of life is secondary. He suggests that, if we begin to know God now, the abundant life has already begun, that is, we begin to experience the kind of life that God lives, the only kind of life that is worth living without end.
This kind of life, then, comes from an intimate relationship with God, implied by the word "know." Genesis 4 informs us that Adam knew his wife, Eve—meaning he and she were intimate—and she had babies. One could say she produced fruit as a result of their close relationship. So, eternal life results from intimate experience in living with God.
What happens if we do not know anything about God? Understanding His names are a good place to begin to know Him. Notice how frequently Jesus mentions the name of God in this prayer: three times. The name represents what Jesus is revealing to us about God. This is a primary way to come to know God—through what Christ has revealed about God.
He asks the Father to keep us through that name (John 17:11). This is done first, by our trusting in it as David did (Psalm 18). When David was in trouble, when he had need, he went to God. In that psalm, he names the names of God that revealed what God would do for him. In a similar way, God will keep, guard, or preserve us because we know Him through the revelation of His name.
Second, we are kept by His name through obedience. Because we understand what those names mean to us, we become obedient to their nature, spirit, or character because they show us what we need to be following or striving for.
— John W. Ritenbaugh