God doesn't just need to patch us up, he gives us new birth and makes us brand new creatures.
But when the kindness and love of God our Saviour appeared, he saved us, not because of righteous things we had done, but because of his mercy. He saved us through the washing of rebirth and renewal by the Holy Spirit.
Chrysostom says this:
For as when a house is in a ruinous state no one places props under it, nor makes any addition to the old building, but pulls it down to its foundations, and rebuilds it anew; so in our case, God has not repaired us, but has made us anew.
A lovely picture of a wonderful gift from God!