NFP and contraception are both methods of birth control. Birth control is just the spacing & planning of children.
The Church does not teach birth control is immoral. The Church teaches that contraception is an immoral
means of birth control. Big difference.
Why?
Each marriage act (act of sexual intercourse) must be unaltered before, during, or after the act. No action may taken to alter the act because each act must be objectively unitive and procreative in order to be authentic and properly ordered as God designed.
Subjectively that particular act may or may not be procreative. For example, if someone is naturally infertile due to time of the month, post-menopause, already pregnant, etc, then an unaltered act of intercourse is objectively procreative but subjectively does not result in conception.
**How does NFP meet this criteria? **In NFP each marital act is objectively unitive and procreative. If you have reason to avoid pregnancy you
do not engage in the act. That respects the objective elements that must be present in every act.
How does contraception fail to meet this criteria? When contracepting a couple engages in the marital act while simultaneously altering the act to nullify it’s procreative element-- either before, during, or after the act. Before-- sterilization, Pill, sponge, diaphram, condom, IUD. During-- withdrawal, masterbatory acts that don’t culminate in intercourse. After- morning after pill, abortion. All of these things alter the act either in anticipation of, during, or after.
NFP says: Don’t want to become pregnant at that time? Abstain and respect the act as God created it because we and the act serve God. Engage in the act when the woman is naturally infertile and never alter the act.
Contraception says: Don’t want to become pregnant? Have sex and mutilate the act because the act serves
us.
NFP is not an alterative to contraception, it’s an alternative to complete abstinence.
For more, go to
www.omsoul.com and pick up some of their resources, especially the Contraception Why Not CD by Janet Smith.