thrustToAttitude

The “R_sp” in the above image is a 33 matrix and as far as i understand euler(0) is assigned it 1st column, euler(1) is assigned its 2nd column and euler(2) is it 3rd column. But, roll_body, pitch_body should be some scaler angles that the vehicle has to turn from its current attitude. Can someone explain me why euler’s column that are 31 vector is directly assigned to roll_sp and pitch_sp. Please, explain me the conversion, it would be a great help. Thank you.