The speech that Carter gives to Gallant in this episode is the same as the one that Dr. Greene gave to him in the Pilot.
Carter's speech to Gallant is a beautiful 'full circle' moment (right down to viewing Carter's reflection in the puddle as he walks out of the hospital) and an emotional pay off for all the devoted fans of the show.
Abby asks Carter how many lives he thinks Dr Mark Greene saved, Carter guesses 1 a shift and 5 shifts a week. Assuming this is accurate and Dr Greene worked at county for 9 years, He saved approximately 2340 lives during his time at County General Hospital.
Carter says he wants to take Abby to "Bill's place", referring to Bill Wilson, the founder of Alcoholics Anonymous.