We must distinguish between the Glory of the Word of God ... and fair-seeming works. ...
Saul seems to be doing the right thing (1 Sam. 15) when he does not kill all the cattle of the Amalekites but keeps the choicer animals for worship. But because God had clearly given the command that all had to be killed, this deed provokes Him to extreme anger. Therefore the fair-seeming work is nothing but an abomination, because it was undertaken against the Word of God.
(Luther's Works, vol. 2:355, as quoted in Steinbronn, Worldviews, CPH 2007, p 125)
Abraham "obeys God's command without arguing." (LW 3:173) He simply cuts the throat of this baneful "Why?" and tears it out of his heart by the roots. He takes reason captive and finds satisfaction in the one fact that he who gives the command is just, good, and wise; therefore, he cannot command anything but what is just, good, and wise, even if reason does not make any sense of it.
(Steinbronn, Worldviews, CPH 2007, p 128)
I'm interested in hearing how others would apply this truth regarding faith to what we might call cases in which casuistry allows for family planning in some instances. Also, how does this apply to the Roman Catholic argument from reason regarding "separating intercourse from procreation" leading to the praise of NFP in exceptional cases. If the Word of God is clear that family planning is an abomination in God's sight, can these cases of casuistry be anything but "fair-seeming" works?