Oxlade-Chamberlain has been training with Arsenal in recent months and thanked the Premier League leaders for helping him to hit the ground running in Glasgow.
“It means a lot,” he said after his dramatic return to competitive action.
“I have to say a big thank you to everyone at Arsenal, giving me the chance to keep my fitness up, and an even bigger thanks to the manager here for giving me the chance to put on this kit and play for this amazing club.
“When you get those opportunities, you want to be able to pay back with moments of quality like that.
“It’s been difficult. Sometimes the way things go in football, especially when you cross that 30-years-of-age barrier, you’re not as valuable as you once were in a business sense.
“I knew I still had a lot to give and training every day for the last three months where I was training gave me the confidence that I can still offer a lot to the game.
“I’m delighted to be here and have the opportunity to do that and help these boys.”
The 32-year-old’s last-gasp goal takes Celtic within a point of Rangers – who drew 1-1 at Motherwell – in second and closer to Hearts, while O’Neill’s side carry that game in hand over both.
“Tonight is a great start for me, but more importantly keeps our goals alive and keeps us going in the right direction,” Oxlade-Chamberlain added.
He says he leapt at the chance to move to Parkhead, with a wee push from his dad.
“It’s an amazing opportunity. When it came up, I didn’t doubt it for one second,” he said.
“My dad’s from an era where this club means a lot. He was straight away telling me ‘I’ll get you in the car and drive you up there myself’.
“It’s a great start, but I know there’s a lot more to it than 13 minutes.”