What is John joyful about? He says it in v.3: "that we have fellowship with us (other Christians) and with the Father and his Son Jesus Christ." There is no joy that can be greater than the intimate fellowship we can have with God and with other Christians. It's not what benefit we can give or get from each other. It is the gift of ourselves--friendship and fellowship. John gives a hint of what that fellowship is like by mentioning our fellowship with the "Father and his Son." It is a familial love, an unconditional love, a love that generates love from the other person. John is saying that we can experience that divine familial love.
How? Through our senses. He keeps repeating the words "we have heard," "we have seen with our eyes," "we have touched with our hands." Christians have a tendency to separate the spiritual things
with fleshly things, and think that anything fleshly is evil or immoral. Of course, if we follow our fleshly desires and make that the object of our joy, then it is truly evil. However, it is clear from this passage that God wants us to enjoy him with our senses.
That is partly the reason why Christ became man. Apostle John explains: "the life was was made manifest to us, that which we have seen and heard we proclaim also to you, so that you too may have fellowship with us" (1:3). Christ is no longer in fleshly form with us. But we can still "see" "hear" and "touch" his presence. His grace is tangible. His love is palpable. His mercy is visible. While we need to make sure that we do not idolize things or people, we are being reminded that God's grace is not theoretical or abstract. It can and should be experienced with our senses
Of course, this principle should not negate the principle in the 2nd commandment, that we should not worship God through images. In the context of what John is writing, experiencing God's grace is through the means of fellowship with other Christians: "If we walk in light, as he is in the light, we have fellowship with one another" (1:7).
Application to education is simple. God has given us children in real flesh. As we seek to bring up our children in the Lord, can we deny that God's grace is real in the way it shapes and molds the minds and the fleshly habits of our children? Absolutely not. Do we become joyful when we see our children not just loving Christ on Sunday only, but also in the way they study, in the way they seek to honor God in the things they do, in the way they enjoy God in their cultural life? Absolutely, absolutely!
In light of all this, we can see that Christmas is a special reminder that Christ took on flesh to make our joys complete, to make our fellowship with God and with one another most meaningful and complete.