The general rule is if they have a different first line they should have separate authorities, so I would not merge these two.
An intrepid editor could create cross links between the two and include a note for the excerpted text, "This hymn was originally part of the longer text, 'Almighty God of truth and love.'" Keeping them obliviously separate as if there is no relationship helps no one.
It looks like both texts may be centos of a larger poem or hymn. You are welcome to do the research.