This question, first, assumes that the way to God had been lost and then seeks to know the reason(s) why Jesus is its restorer. To answer your question, I have to respond to your assumption and then provide reasons why Jesus is this restorer.
1. God’s description of us
God said that He made us in His image. This means that He made us in such a way that whenever He sees us, He sees Himself. That’s the more reason why He established a relationship on earth: to reveal His being to us. God is a relational being and we are His representatives on earth.
2. How we fell from that description
But, we moved away from how God defined us. Therefore, God could no longer see His image in us, in the sense that He could not see Himself through us anymore. We blocked it with our image. We did not do what He had determined for us in keeping with how He defined us. Instead, we did what we ourselves wanted to do. And when we launched into our own definition, it broke His definition over us.
3. Why Jesus came
As we lived with our own definition, we could not recognize God for who He was/is anymore. We deified ourselves, by becoming the ones defining reality. So Jesus came to reveal to us that there’s only One being necessary for defining all reality. His name is I AM
4. Why God saved us
As God no longer saw His image in us, He condemned us to death because He knew we would malfunction apart from Him. But He later reached out in love to bring us to the function we have in Him, in order to show us our status apart from Him. He knew what we would become apart from Him.
5. Who’s Jesus? (His nature)
As we moved away from God’s definition, our nature became corrupt. And how we defined reality conformed to this corrupt nature of ours. But Jesus was different. His nature wasn’t like ours. He is good, and it is by this He defines reality. This is the definition most worthy of worship, the one we long so much for.
6. Who’s Jesus? (His resurrection)
Jesus’ earthly mission ended on the cross; He had completely revealed who God was/is, by displaying His love towards us. He was then laid in a tomb. But three days later, He rose from it. He is still alive! The resurrection combines every piece of revelation we know of Jesus throughout His ministry until the cross. It tell us He’s God.