The full passage explains it well.
‘One who has shaped this world is ever its lord:Our errors are his steps upon the way;
He works through the fierce vicissitudes of our lives,
He works through the hard breath of battle and toil,
He works through our sins and sorrows and our tears,
His knowledge overrules our nescience;
Whatever the appearance we must bear,
Whatever our strong ills and present fate,
When nothing we can see but drift and bale,
A mighty Guidance leads us still through all.’
It means that there is a hidden Guidance in life, a Grace that works from behind even though we cannot see it or understand its working. Hence we must learn to trust and have faith that whatever be the outer appearance the Divine Grace will carry us through it all towards our true destiny.
Affectionately,
Alok Da