The difference is that we are being saved from our own sins rather than from a world that has fallen to sin. Jesus did not come down to Earth to rain fire and brimstone upon the unworthy. He did not come a worldly king to rule our existence. Instead He came to us to save everyone, to minister to the lowly and forgotten, to bring salvation to those full of sin … like me.
The waters of Noah's flood wiped away the sinful from the world. The waters of Baptism wipe away my own sins. In both cases, the single act is not enough on its own to eliminate sin entirely. Rather, sin continues to find ways to return, ways to bring death back into our holy lives. Yet Jesus shows that He is always there for us, ready to help when we simply ask.
He didn't say that the kingdom of God was coming soon, but that it was "at hand," there and then, here and now. The kingdom of God surrounds us even now. We just need to accept God's covenant with us.