Jesus Christ is God as man and has God’s character. As man, Jesus can experience life with the rest of humans and show man God’s character — in person (1:14). As we’ll see later, Jesus has done a lot of stuff — even John knew that Jesus’s acts surpass John’s accomplishments (1:15)!
Part of the reason that John credits Jesus more than himself is that Jesus provides grace and truth, which he’ll demonstrate much later. Jesus is the ultimate source of grace and truth (because he’s God himself!). As we’ll see in later passages, when we trust in him, we receive his fullness and grace (1:16-17).
Jesus’s appearance was also a pretty unique event. In fact, John 1:18 likely refers to how no one saw God’s true form while on Earth (before Jesus). All other representations (burning bush) were limited representations of God. Note that from the Interlinear Bible, the word “see” (Strong 3708) can also mean “perceive”, which also makes sense in context because many of Jesus’s teachings were concepts that were either unfamiliar or barely hinted on beforehand.