And did those feet in ancient time
Walk upon England's mountains green?
And was the holy Lamb of God
On England's pleasant pastures seen?
And did the Countenance Divine
Shine forth upon our clouded hills?
And was Jerusalem builded here
Among these dark satanic mills?
Bring me my bow of burning gold!
Bring me my arrows of desire!
Bring me my spear! O clouds, unfold!
Bring me my chariot of fire!
I will not cease from mental fight,
Nor shall my sword sleep in my hand
Till we have built Jerusalem
In England's green and pleasant land.
Contrasting with the repetition of violent tools, Blake describes a “mental fight.”  This means Blake understands that the challenges faced cannot only be solved through force, but also through intelligence or emotion. 
 This follows his reasoning in his poem  London , in which he powerfully describes the terrible lives of people trapped in poverty, but also refers to  mind-forged manacles  — his belief that we are also trapped in our own negativity and limitations. Here he is asserting his determination to overcome inner emotional and mental barriers.
And Did Those Feet In Ancient Time