There's a cross inscription in the last four notes, so this particular "How great Thou art" seems to point to Jesus' death on the cross for the sake of all sinners as one specific example of that greatness. This is also described in the third verse of the hymn:
But when I think that God, His Son not sparing,
Sent Him to die, I scarce can take it in -
That on the cross my burden gladly bearing
He bled and died to take away my sin;