Taught of God (didaktoi theou). A free quotation from Isa 54:13 with this phrase in the lxx. There is here the ablative case theou with the passive verbal adjective didaktoi (Robertson, Grammar, p. 516). In 1Th 4:9 we have the compound verbal theodidaktoi. The same use of didaktos with the ablative occurs in 1Co 2:13.
And hath learned (kai mathōn). Second aorist active participle of manthanō. It is not enough to hear God’s voice. He must heed it and learn it and do it. This is a voluntary response. This one inevitably comes to Christ.