Umar Farouk Abdulmutallab told a Detroit courtroom Wednesday that the bomb was a "blessed weapon to save the lives of innocent Muslims."
Abdulmutallab has pleaded guilty on the second day of his trial to charges that include conspiracy to commit terrorism and attempted murder.
He says he tried to blow up Northwest Airlines Flight 253 with nearly 300 people on board on Christmas 2009.
The bomb didn't work, but Abdulmutallab was badly burned. Hours later in the hospital, he told the FBI that he was working for al-Qaida in Yemen.