The text is from Isaiah 53:3: "He was despised and rejected by men; a man of sorrows, and acquainted with grief; and as one from whom men hide the faces he was despised, and we esteemed him not." and from Isaiah 50:6: "I gave my back to those who strike, and my cheeks to those who pull out the beard; I hid not my face from disgrace and spitting."
An-other thing I didn't notice until I started following along with the notation is the cross-like figure inscribed here with "he was despised."
I first ran across this cross-inscribing feature in John Eliot Gardiner's Bach: Music in the Castle of Heaven, where he points out how Bach does this in Christ lag in Todes Banden, BWV 4:
I'm not sure if it was Handel's intent here (I don't know how well-known this cross-inscription technique was in the 1700s), but it does provide an example of one of the forms in which Christ was despised - the crucifixion.