Socrates (469–399 B.C.E) was a popular Greek philosopher who believed that all humans were automatically born with good virtues.
In other words, the line can be understood in the view of Socrates as saying 'the good deeds hidden within a person only need to be opened up not taught,' which includes such deeds as honesty, generosity, kindness, etc.
"a testimonial" would most likely include positive information about one side of an issue, although it should be noted that this is not always the case with testimonials.
