The joy of the Lord, that joy which comes from knowing our sin is pardoned.
Can I say-- 'O happy day, O happy day When Jesus washed my sins away ?' Then I have spiritual strength, for the joy of the Lord is my strength.
He has forgiven me, He has washed me from my sins in His own blood; how can I grieve Him?
How can I pain Him by yielding to temptation?
How can I ever risk losing the joy of my heart by going contrary to His will?
I am joyful because I am forgiven, and I am strong because I am joyful.
Here then is the highest kind of strength, and it is a strength within the reach of all.

Bodily strength some of us can never attain.

We are born with weakly bodies, we have grown up delicate and frail, we could no more transform ourselves into strong, powerful men, than we could make ourselves into elephants.
There was a man who lived in Greece long before Hezekiah, who was determined to make his nation the strongest nation on earth; he was resolved that it should consist of mighty giants in strength, and that not one delicate or weak man should be found amongst them.

But what did Lycurgus find himself obliged to do in order to secure his end?
He was compelled to have every infant carefully examined as soon as it was born, and if a child had the least appearance of delicacy, he took it from its mother, and sent it to some lonely cave on the hill-side, where it was left to die of cold and hunger.

He found that it was not possible to turn a puny delicate child into a strong man.
Bodily strength then is beyond the reach of many men; weak they were born, weak they live, and weak they will die, nothing will alter or improve them.
Nor can strength of mind be attained by many.