your probly not gonna like my answer, and i really dont know if anyone that agrees with me on this becuase i havent asked around...
my simple answer is that, HE DID.
i cannot fully prove it, but heres why i believe this.
john 15.5
"i am the vine, ye are the branches: He that abideth in me, and I in him, the same BRINGETH FORTH MUCH FRUIT:..."
ephesians 5.9
"for the fruit of the spirit is in ALL GOODNESS, AND RIGHTEOUSNESS AND TRUTH"
i do not believe that anyone born again has any sin nature obligating them to sin and do evil things, rather a born again christian has a much stronger power inside them working, and causing them to go and do GOOD THINGS, RIGHTEOUS THINGS, AND TRUE THINGS. becuase if your in God have an inner pressure and influence to bear fruit for the Lord.
now there are things that pressure us to sin, but i dont beleive its the sin nature that obligated you to sin before you knew Christ.
old habits, addictive pleasures, mistakes, ignorance, etc, but that is not the sin nature. those are things you grow out of and throw off through Christ.
i dont believe anyone can say that we are obligated to a sin nature or to sin at all as a christian.
romans 6.22
"But now being MADE FREE from sin, and become servants unto God, YE HAVE YOUR FRUIT UNTO HOLINESS, and the end everlasting life."
after a man is born again, aside from the desires of his body, old habits, ignorance etc, he has more pressuring him TO DO GOOD, than to do evil.
there are alot of IFS ANDS OR BUTS, but the point is, basicly, you do have more pressuring you to do good, than to do evil.
we were made free from sin, i dont believe we can say that we have a sin nature after Christ, nor do i beleive it can said that a Christian must live in sin at all after the changing power of God in his life has taken process.