Sei vor uns sim Fleische kräftig!
Das Vermögen in uns Schwachen
Stark zu machen!
Be strong for us in the flesh!
To strengthen the power
In us who are weak!
"Streite, siege, starker Held!", a paraphrase of stanza 6 of "Nun komm, der Heiden Heiland," by Martin Luther (1523), who was translating "Veni Redemptor gentium," by St. Ambrose. According to the liner notes to the Gardiner recording above, "Streite, siege starker Held!" was composed by an unknown librettist for J. S. Bach's Cantata for the First Sunday in Advent BWV 62 (Nun komm, der Heiden Heiland). Luther's sixth stanza, as reproduced in The Canterbury Dictionary of Hymnology (I haven't checked this against Jenny), ran as follows:
Der du bist dem vater gleich,
fur hynnaus den syeg ym fleisch,
das dein ewig gots gewalt
ynn unns das kranck fleysch enthallt.