I´m looking for the source of these lines by Longfellow:

Thou seemeth human and divine,
The highest, holiest , manlord thou,
Our wills are ours, we know not how,
Our wills are ours, to make them thine.
The heights of great men reached and kept
Were not attained by sudden flight,
But they, while their companions slept,
Were toiling upward in the night.

Can anybody help me? Thanks!

The ladder of ST Augustine
.
[eir.library.utoronto.ca]