Verses 3 and 4 are being provided together since verse 4 is short and simple, giving two days to spend memorizing verse 3 while also reviewing and strengthening the recall of verses 1-2. (Are you using flashcards to carry the verses around with you each day?)
3 that which we have seen and heard we proclaim also to you, so that you too may have fellowship with us; and indeed our fellowship is with the Father and with his Son Jesus Christ. 4 And we are writing these things so that our joy may be complete. (ESV)
3 That which we have seen and heard declare we unto you, that ye also may have fellowship with us: and truly our fellowship is with the Father, and with his Son Jesus Christ. 4 And these things write we unto you, that your joy may be full. (KJV)
Greek:3 ὃ ἑωράκαμεν καὶ ἀκηκόαμεν, ἀπαγγέλλομεν καὶ ὑμῖν, ἵνα καὶ ὑμεῖς κοινωνίαν ἔχητε μεθʼ ἡμῶν. καὶ ἡ κοινωνία δὲ ἡ ἡμετέρα μετὰ τοῦ πατρὸς καὶ μετὰ τοῦ υἱοῦ αὐτοῦ Ἰησοῦ Χριστοῦ. 4 καὶ ταῦτα γράφομεν ἡμεῖς, ἵνα ἡ χαρὰ ἡμῶν ᾖ πεπληρωμένη.
Transliterated Greek: 3 ho heōrakamen kai akēkoamen, apangellomen kai hymin, hina kai hymeis koinōnian echēte meth’ hēmōn. kai hē koinōnia de hē hēmetera meta tou patros kai meta tou huiou autou Iēsou Christou. 4 kai tauta graphomen hēmeis, hina hē chara hēmōn ē peplērōmenē.
Literal Word for Word Translation: 3 what we have seen and heard we announce also to you, in order that you also may have fellowship with us. And indeed our fellowship is with the Father and with his Son Jesus Christ. 4 And we write these things in order that our joy may be complete.
Commentary: With the parenthetical of verse 2 about the “word of life / eternal life” complete, verse 3 picks back up from verse 1 by repeating John’s personal testimony of having physically experienced this “life.” Notice there is an emphasis on seeing. In each of the first three verses John mentions seeing the “life.” Again, this is to emphasize the physical reality of the Messiah. But even further, in verse 3 John repeats the “having heard” from verse 1 to point to that which was being proclaimed. It will be seen in verse 5 that what is being proclaimed is a message. A message is heard. As much as Jesus has a human existence and can be seen, He is the incarnate Logos/Word of God. He is to be heard. Jesus physically died on the cross and physically rose from the grave (1 Cor. 15:3-8) to obtain our salvation, yet it is by hearing the Word of Christ, that we enter into salvation (Rom. 10:13-17; Jn. 10:27-28; Eph. 1:13-14).
The word of life is being proclaimed so that the hearers of the message can join in fellowship with John and other early Christians, a fellowship that includes the Father and His Son, Jesus Christ. We often hear that it is not about a religion, but about a relationship. John knows that without fellowship with those who are united by the Spirit, a person is not part of the one body. This has implications for those who do not have fellowship with other Christians. Those who deny the need to have fellowship have cut themselves off from the body. They may declare others as hypocrites as their excuse, but reality is that an arm or a leg cut off from the body is useless – it has no life and no function. This also means that those who are not able to participate in fellowship because of circumstances beyond their control, such as health, job, or whatever, need to be included in a fellowship in some way. The reality is that all who are in Christ are one big family and will be in fellowship in eternity. Refusing fellowship now, is in essence refusing Christ. Some will argue that it is only by the cross that we are saved and fellowship is not important. However, that is selfish thinking and contrary to the theme of the whole Bible. God’s people are a community in which Christ is the center. Isolated people can be saved, however saved people do not want to be isolated. It is like saying one is married and yet has never had a relationship with the spouse. For those who are in ill health, members of the church need to visit and bring the body of believers to them.
Lastly, John says his letter is being written so that the joy of those proclaiming Christ with him may be complete. There is no greater joy in the Christian life than to see others come into it. It isn’t about building a big congregation, but about seeing people saved! That they will come to experience the peace and joy that believers have (Rom 4:17; 15:13; 1 Pet. 1:8-9; Gal 5:22). That joy results in believers wanting to be in fellowship with one another. It is a blast to have a meal or enjoy activities together with fellow believers. It is so much more fun than getting blitzed at a party and ending up with a hangover the next morning and spending time with friends that only want to share misery. Why not get drunk in the Spirit rather than with wine? (Eph. 5:18)