Lutherans believe that Jesus is the only way to get to a trusting relationship with God and eternal life. We don’t believe that just “living a good life,” no matter how good it is, will be good enough to earn those great gifts.
The logic of Jesus Only
If we could live lives that were good enough to earn a place before God, logic would tell us that God would never send His Son Jesus as our Savior. In fact, God would be at cross purposes with Himself by sending Jesus if we could earn our own place. If we could do it, God sending Jesus would just make us lazy and less motivated to earn our place before Him.
The human problem
The human problem is sin. We all have it as a result of the first sin of Adam and Eve that created a sort of sinful mutation that was handed down from generation to generation. If we are conceived, we can’t help but be sinful. It is in our DNA.
The heavenly solution
In order to solve our human problem, God inserted Himself in the person of Jesus into our history as the only perfect human being to ever live on the earth. We believe that Jesus lived the perfect life that we couldn’t, and then died on the cross to allow for the transfer of His “perfectness” (righteousness) to the rest of the human population for all time.