As Dawn said, the rules have changed with the advent of the Gospel. Getting into Old Testament justification is neither necessary (since it is no longer relevant) or prudent (since the answers are nowhere to be found).
The Catholic Church teaches that the legal prescriptions of the Mosaic Law are obsolete, but they were at one point adequate for salvation.
Pope Eugene IV, Council of Florence, Session 11, 1442: "It firmly believes, professes and teaches that the legal prescriptions of the Old Testament or the Mosaic Law, which are divided into ceremonies, holy sacrifices and sacraments, because they were instituted to signify something in the future, although they were adequate for the divine cult of that age, once our Lord Jesus Christ who was signified by them had come, came to an end and the sacraments of the New Testament had their beginning."