Car takes ALOT to move it...

Ok...so today I had the car running and decided to see if it would move under its own power. So I backed it out of its spot in the driveway and onto the street, where I placed it down into 1st gear on the 727. I let off the brake, but the only way to get the car to move at all is to give it some gas (read...quite a bit of gas), and then it will inch forward. I didn't get on it at all or even try pushing the pedal down too far, but I was just wondering what could possibly cause the car to not want to move at idle/1500 or so RPM.