This quote is very likely spurious, because it seems to disparage theologians, though it is attributed (again, without an exact reference) to St. Ambrose by the prominent lay Catholic theologian Ralph McInerny, in What Went Wrong with Vatican II: The Catholic Crisis Explained p. 96, where he explains "That means among other things that one need not be a theologian in order to be a Christian, or a saint."
St. Ambrose did write (Commentary on St. Luke's Gospel bk. 5 n. 46, p. 133):
He came down to meet our wounds, so that by associating with us He might make us sharers in His heavenly nature.
St. Augustine said in a Christmas sermon (xiii de Temp., as quoted by St. Thomas Aquinas, Summa Theologica III q. 1 a. 2 co.):
God was made man, that man might be made God.
factus est Deus homo, ut homo fieret Deus.