"And this is the will of Him who sent Me, that everyone who sees the Son and believes in Him may have everlasting life; and I will raise him up at the last day." John 6:40

Believes here is the same verb that Jesus used in John 3:16. "Vine's Expository Dictionary of Old and New Testament Words" tells us the Greek word is,
"PISTEUO: to believe, also to be persuaded of, and hence, to place confidence in, to trust, signifies, in this sense of the word, reliance upon, not mere credence."
Strong's Exhaustive Concordance of the Bible adds "...by implication to entrust (especially one's spiritual well-being to Christ)..."

This verb (believe, believes, believed) is used 45 times in the Gospel of John. Of the 45, Jesus used PISTEUO 25 times and others used the word 20 times. (I have not included other verbs, noun or adverb words for believe.) I have brought in these numbers to emphasize that eternal life is for those who believe. And that belief is to trust in, rely on, entrust their spiritual well-being to Jesus. It is not just knowing about Jesus, God's only begotten unique Son.

Jesus says in John 17:3,
"And this is eternal life, that they may know You, the only true God, and Jesus Christ whom You have sent."

'...that they may know You, the only true God, and Jesus Christ...'
This is spiritual knowledge. Scripture tells us-- It is obtained by acquaintanceship with God:
"Let us know,
Let us pursue the knowledge of the LORD.
His going forth is established as the morning..." Hosea 6:3

The condition of receiving is obedience:
"Jesus answered them (the Jews) and said, 'My doctrine is not Mine, but His who sent Me. If anyone wants to do His will, he shall know concerning the doctrine, whether it is from God or whether I speak on My own authority.
He who speaks from himself seeks his own glory; but He who seeks the glory of the One who sent Him is true, and no unrighteousness is in Him.'"
 John 7:16-18

It frees the soul from error:
"Then Jesus said to those Jews who believed Him, 'If you abide in My word, you are My disciples indeed. And you shall know the truth, and the truth shall make you free.'" John 8:31-32

And what is the Believer's attitude toward this knowledge?
Believers are not to be puffed up:
"Knowledge puffs up, but love edifies." 1 Corinthians 8:1

Believers should grow in knowledge:
The apostle Peter tells us in 2 Peter 3:18, "But grow in the grace and knowledge of our Lord and Savior Jesus Christ, to Him be the glory both now and forever. Amen."

Believers should add to their knowledge:
Peter gives a list of attributes that will be fruitful in the knowledge of our Lord. Read 2 Peter 1:5-8. Verse 5 says, "But also for this very reason, giving all diligence, add to your faith virtue, to virtue knowledge."

Paul tells Believers in Philippians 1:9-10, "And this I pray, that your love may abound still more and more in knowledge and all discernment, that you may approve the things that are excellent, that you may be sincere without offense till the day of Christ."

Growing in the knowledge of God comes in many forms. There is Bible centered preaching, reading the Scriptures, Bible study groups, songs, devotionals and personal study. We have the indwelling Holy Spirit to lead, guide and open up God's word to us. The key is commitment to a time devoted to getting to know our Most Holy God.

Considering eternal life. Read again John 6:40 and John 17:3. This is the order, believe and come to know. Believe in Jesus and He shows us the Father. "...He who has seen Me has seen the Father..." John 6:9

Thank you Father for Your great love that sent Your Son, our Savior, in whom we believe.  In believing we have eternal life.  We love and adore You. Amen