The meaning of "pagsubok" is trials and "wag ka susuko at iyong laban" means fight all the trials w/o giving up.
This song is one of my favorite and the lyrics is very meaningful to me the real meaning of the song is whatever problems or trials we may face in the journey of life God will always be by our side.
Even though we may lure and hide behind a dark past even when hope seems uncertain when life seems to fall down on us we must never give up and we must fight till the end.
Pagsubok - "Trials or Problems"
Wag susuko - "Never give up"
At iyong labanan - "And Fight" the trials and problems in life.