"This means everlasting life, their taking in knowledge of you, the only true God, and of the one whom you sent forth, Jesus Christ." (NWT)
Many have the mistaken belief that one just needs to 'believe in Jesus and you will be saved'. But in actuality, this makes light of serious Bible study and demonstrates that most of these people who profess religious faith give little thought to why they believe what they do or to whether there is a reasonable basis for their faith.
John 17:3 shows that more than simply 'believing in Jesus' is required in order to gain "eternal life".
The Bible likens the searching for "the very knowledge of God" to "silver, and as for hid treasures". (Prov. 2:5) That is because when one finally begins to discover the truths to the mysteries of life in the Bible they will have more peace of mind along with the knowledge about God that can lead to "eternal life". (John 17:3)
Jesus said: “Happy are those conscious of their spiritual need.” (Matthew 5:3)
To fill our spiritual need, we can imitate the example of the Beroeans. Luke wrote that they “received the word with the greatest eagerness of mind,” and that they were “carefully examining the Scriptures daily as to whether these things were so.” (Acts 17:11)
When "carefully examining" John 17:1-3, we can learn a few basic truths. Jesus prayed to the Father: "FATHER, .... this is eternal life: that they may know you, the only true God, and Jesus Christ whom you have sent." - NIV
A prevalent teaching in the world today is the Trinity Doctrine or that Jesus is God. Yet at John 17:3, the Father alone is not only very clearly identified as the only true God, but Jesus Christ is again pointedly and specifically excluded from that identification ("AND Jesus Christ whom YOU [the only true God] have sent").
To understand that Jesus is not God is a tremendous bit of information in knowing who Jesus is and who God is. Especially if it means "eternal life"!
One would reasonably conclude that it would also be important to know what God's name is if it means "eternal life". (Also see: God Has a Name!; g04 1/22 pp. 3-4; Watchtower Online Library)
Sincere Bible students could and should use the import of John 17:3 as an incentive to further Search for Bible Truths. Much can be gained when one finally learns the accurate knowledge contained in the Bible. (Also see: "What Does the Bible Really Teach? - What Is the Truth About God?"; bh chap. 1 pp. 8-17; Watchtower Online Library)
For much more concerning John 17:3, see:
If the Father is the "only true God" (John 17:3), does that mean that Jesus is a false god? (Search For Bible Truths)
"The Only True God" (Examining the Trinity)
Jn 17:3 "Taking in Knowledge" (Defending the New World Translation)
John 17:3 (Bible Translation and Study; 2nd Scriptural listing on page)
How Does John 17:3 Show That The Trinity Doctrine is NOT a Bible Teaching? (Search For Bible Truths)
Gods or only one God? (Search For Bible Truths)
Is Jesus God or the Son of God? (Search For Bible Truths)
How is Jesus a god? (Search For Bible Truths)