[35] Why was this? Because the virtue acquired by teaching, which Abraham pursues, requires many things, both such as are legitimate according to prudence, and such also as are illegitimate according to the exegetical contemplations of preliminary instruction. And there is also a virtue which is made perfect by practise, to which Jacob appears to have been devoted; for exercises consist of many and various dogmas and doctrines, some leading and others following, some leading the way, and others arriving later, and bringing at one time more serious, and at other times lighter labours.