"Mein ganzes Herz erhebet dich" (My whole heart magnifies You) is the beginning of German hymns to a melody from the 16th century, which paraphrase Psalm 138.
[1] This psalter was used by the Huguenots, who were persecuted in France for more than two centuries but nonetheless sang psalms and derived strength from doing so.
[1] Like other melodies of the Psalter, it was simple, spanning only an octave, and in easy rhythm of notes in only two values.
[2] The Reformed pastor Matthias Jorisson [de] wrote new texts in German to the Genevan melodies, published first as Neue Bereimung der Psalmen in 1798, paying closer attention to the biblical originals than the Genevan Psalter, expanded in 1806 to Die Psalmen Davids neu übersetzt und in Reime gebracht.
[3] This hymn appears in the Gotteslob of 2013 as GL 143, in the section "Gesänge zur Eröffnung", suitable for the opening of a service.