Modern writers have proposed many valuable aspects of background for the “Word,” but probably the most obvious is what the “Word” was in the Old Testament: God’s word was the law, the Scripture he had given to Israel. John probably wrote his Gospel especially for Jewish Christians. Opponents of these Jewish Christians had probably kicked them out of their synagogues and claimed that they had strayed from God’s Word in the Bible. Far from it, John replies: Jesus is the epitome of all that God taught in Scripture, for Jesus himself is God’s Word and revelation.
John probably alludes to one story in particular, the account of when Moses went up to receive the law the second time in Exodus 33 and 34. Israel had broken the covenant and God had judged them; now he gives Moses the law again but does not wish to “dwell” with Israel. Moses pleads with God to dwell with them, and then pleads with God to show him his glory. “No one can see my full glory,” God told him, “but I will show you part of my glory, and make my goodness pass before you.”
As God passed before Moses, Moses witnessed an astounding spectacle of glory; but especially God revealed his “goodness,” his holy character, to Moses. As he passed before Moses, he described himself as “abounding in covenant love and covenant faithfulness,” which could be translated, “full of grace and truth.” And after God was finished revealing his character, Moses protested, “God, if that is the way you are, then please forgive us and dwell with us.” And God promised to do so.
Some thirteen centuries later, the apostle John spoke of himself and his fellow eyewitnesses of Jesus in a manner like Moses. “We beheld Jesus’ glory,” he said, “full of grace and truth” (Jn 1:14). He builds to a climax in 1:17: “For the law was given through Moses, but grace and truth came through Jesus.” To be sure, God revealed his grace and truth to Moses when he gave him the law; but Moses saw only part of God’s glory, only part of his grace and truth. “No one has seen God at any time,” John reminds us, alluding back to God’s warning to Moses that he could not see all of God’s glory; but now “the only God, who is in the Father’s bosom, has revealed fully God’s character” (1:18). Moses saw part of God’s glory, but those who walked with Jesus saw all of God’s glory, for to see him is to see the Father (Jn 14:7).
Whole book context explains the point here more fully. God’s glory is revealed in various ways in Jesus (2:11; 11:4), but the ultimate expression of God’s glory here is in the cross and the events that follow it (12:23-24). We see God’s heart, and most fully understand what God was like, when we look at the cross where God gave his Son so we could have life.