I saw this in Boyhood and Beyond: Practical Wisdom for Becoming a Man by Bob Schultz and didn’t realize it was a hymn:

Be strong!
We are not here to play, to dream, to drift;
We have hard work to do and loads to lift;
Shun not the struggle, face it, ’tis God’s gift.
Be strong, be strong, be strong!

Be strong!
Say not the days are evil—who’s to blame?
And fold the hands and acquiesce—O shame!
Stand up, speak out, and bravely, in God’s Name.
Be strong, be strong, be strong!

Be strong!
It matters not how deep entrenched the wrong,
How hard the battle goes, the day, how long;
Faint not, fight on! Tomorrow comes the song.
Be strong, be strong, be strong!

~ Malt­bie D. Bab­cock, 1901

This book of the law shall not depart out of thy mouth; but thou shalt meditate therein day and night, that thou mayest observe to do according to all that is written therein: for then thou shalt make thy way prosperous, and then thou shalt have good success. Have not I commanded thee? Be strong and of a good courage; be not afraid, neither be thou dismayed: for the LORD thy God is with thee whithersoever thou goest. Joshua 1:8-9

Conditions for receiving strength.