Notice this line in the song:
Thou and Thou only first in my heart. High King of Heaven, my treasure Thou art.
Oh, that Jesus would truly be first in all of our hearts. And not “first” in the sense of priority. The Savior doesn’t want to be first if that means family will be a close second. He doesn’t belong on such a hierarchy. No, Christ does not want to be first above all things; He wants to be first in all things. He doesn’t belong on a list of priorities. What it means for us to have Him and Him alone first in our hearts is that He is the priority.
Not only would that be honoring to Him and appropriate because of His worth–He is our Savior and our God–but it also is for our joy. Just as the penman said to Him, “my treasure Thou art”, so does it mean for us that if He were first in our hearts, He would be our treasure. And what brings us more joy than knowing Him?
Paul wrote that he counted everything as loss because of the surpassing worth of knowing Christ Jesus our Lord. There is no greater joy for someone who has a new heart than to know Christ more and more. So, Jesus’s desire is to not only be our Lord but to also be our treasure. He wants for us to value Him more than anything in this world. It honors Him as He deserves, and it blesses us with rich joy.