Surely God is My Salvation
Many will recognize this as The First Song of Isaiah. I was planning the mid-week Lenten services for this year, based upon the Service of Prayer and Preaching, and it called for a canticle based on Isaiah 12:2-6. None of the readily available sources in my congregations had a hymn based on this text except for one with a difficult tune out of a hymnal supplement that only one of my congregations had; and this one was even copyrighted, so it couldn't easily be copied for use at the other congregation. So, I sought to write a hymn myself based on this text for use in the services.
How did I settle on those tunes? Well, as I wrote the first phrase, I wrote it singing it to the first tune, without realizing what tune I was using. So, I scrambled to find the tune, writing the second and third phrases and getting the meter, then searching a hymnal index for the tunes that matched that meter. While looking at all the tunes in that meter in the index (a grand whopping total of 4), I thought that the second tune also matched the words well enough.