I didn't know until recently that Wenceslas actually existed, though he was a Bohemian Earl, not a king. Wenceslaus I or Vaclav the Good was Duke of Bohemia from 921 until his death when he as killed with a lance by his brother Boleslaus the Cruel. After his assassination, he was posthumously declared a monarch.
Apparently, Wenceslas was well known for his kind acts. He would rise up from his bed every night and with only one chamberlain, or "page," went around to God's churches and gave generously to widows, orphans, those in prison and those afflicted by difficulties. He was considered the father of all the wretched and the song reflects his good acts.
The story of the Christmas carol is that Wenceslas is out with his page and sees a poor man gathering "winter fuel." The monarch and the page bring food, wine and pine logs to the poor man even though there were "rude winds...and bitter weather."
At one point the page says to the monarch:
"Sire, the night is darker now
and the wind blows stronger
Fails my heart I know not how
I can go no longer."
Wenceslas answers the page:
"Mark my footsteps, good my page
Tread though in them boldly
Thou shalt find the winter's rage
Freeze thy blood less coldly."
As the page followed in his master's footsteps, he found that "heat was in the very sod, which the saint had printed."
This is the part that struck me so much this year, Wenceslas telling the page to mark his footsteps and the page feeling that heat was in the very sod where the saint has walked. It reminded me of these verses:
"As ye have therefore received Christ Jesus the Lord, so walk ye in Him." Colossians 2:6
"For in Him dwelleth all the fulness of the Godhead bodily." Colossians 2:9
There are times in our lives where the "winter's rage" of life blows too strongly against us and we don't know how we can go on. But the Lord calls us not to walk in our own strength, but in the "power of His might." (Ephesians 6:10.) We are called to plant our feet in His footsteps, as it were, and trust Him for the strength and power to do what He has called us to do. When we do, like the page in the carol, we will know His power, His strength and His enabling to "mark" His footsteps.
"For it is God which worketh in you both to will and to do of His good pleasure."