When Mariano Rivera was growing up poor in Panama, he wanted to be a mechanic, but fate intervened and he ended up as one of the greatest relief pitchers in baseball.

Rivera, who retired from the New York Yankees last year after nearly 20 years in Major League Baseball and helping the Yankees win four championships, credits God for his remarkable life.

He lays it all out in his book, "The Closer," which will be released Tuesday.

PHOTOS: Rivera Retires After 18 Years

A member of an adult baseball league, Rivera was called in from the outfield because his team needed some outs.

"I wasn't supposed to be pitching in that game. I wasn't supposed to pitch period," he said, speaking in an interview with "Good Morning America" co-anchor Robin Roberts.

When he came to America to pursue his dream he didn't even speak English, and he smiled when he recalled his reaction to being called to play for the big leagues.

"I was in bed, jumping in bed … like a little kid. Robin it was something special for me. I will never forget that moment," he said.

On the field at Yankee Stadium at his final game last year, he sobbed next to longtime teammates Derek Jeter and Andy Pettitte.

He said the reality hit him like a ton of bricks.

"You know, I was strong for the whole year. But at that moment, I couldn't hold it no more," the 13-time All-Star closer said.

Rivera, 44, has already embarked on a new chapter of his life.

He and his wife, Clara - whom he met in kindergarten - restored a church in New Rochelle, N.Y. Clara Rivera is the pastor at Refugio de Esperanza - or Refuge of Hope church.

Rivera agreed that he's gone from saving games to saving souls.