Wonderful question with a beautiful answer from our faith…
Here’s a quote from the Catechism of the Catholic Church… it’s long, but read it all… (see this link to the full section in the Catechism)
The fecundity of marriage
Fecundity is a gift, an end of marriage, for conjugal love naturally tends to be fruitful. A child does not come from outside as something added on to the mutual love of the spouses, but springs from the very heart of that mutual giving, as its fruit and fulfillment. So the Church, which is "on the side of life,"151 teaches that "it is necessary that each and every marriage act remain ordered per se to the procreation of human life."152 "This particular doctrine, expounded on numerous occasions by the Magisterium, is based on the inseparable connection, established by God, which man on his own initiative may not break, between the unitive significance and the procreative significance which are both inherent to the marriage act."153
Called to give life, spouses share in the creative power and fatherhood of God.154 "Married couples should regard it as their proper mission to transmit human life and to educate their children; they should realize that they are thereby cooperating with the love of God the Creator and are, in a certain sense, its interpreters. They will fulfill this duty with a sense of human and Christian responsibility."155
A particular aspect of this responsibility concerns the regulation of procreation. For just reasons, spouses may wish to space the births of their children. It is their duty to make certain that their desire is not motivated by selfishness but is in conformity with the generosity appropriate to responsible parenthood. Moreover, they should conform their behavior to the objective criteria of morality:
When it is a question of harmonizing married love with the responsible transmission of life, the morality of the behavior does not depend on sincere intention and evaluation of motives alone; but it must be determined by objective criteria, criteria drawn from the nature of the person and his acts, criteria that respect the total meaning of mutual self-giving and human procreation in the context of true love; this is possible only if the virtue of married chastity is practiced with sincerity of heart.156
"By safeguarding both these essential aspects, the unitive and the procreative, the conjugal act preserves in its fullness the sense of true mutual love and its orientation toward man’s exalted vocation to parenthood."157
Periodic continence, that is, the methods of birth regulation based on self-observation and the use of infertile periods, is in conformity with the objective criteria of morality.158 These methods respect the bodies of the spouses, encourage tenderness between them, and favor the education of an authentic freedom. In contrast, “every action which, whether in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible” is intrinsically evil:159
Thus the innate LANGUAGE that expresses the total reciprocal self-giving of husband and wife is overlaid, through contraception, by an objectively contradictory LANGUAGE, namely, that of not giving oneself totally to the other. This leads not only to a positive refusal to be open to life but also to a falsification of the inner truth of conjugal love, which is called upon to give itself in personal totality. . . . The difference, both anthropological and moral, between contraception and recourse to the rhythm of the cycle . . . involves in the final analysis two irreconcilable concepts of the human person and of human sexuality.160
So, to answer your question in layman’s terms… the “rhythm of the cycle” (now most often referred to as “Natural Family Planning”) is designed by God. It doesn’t go beyond God’s creation or plan. Artificial methods of birth control (ABC) say to God “I want sex on MY terms”… and NFP says “I trust you, God”.
The mentality of the use is a big issue… NFP can, of course, be used with a “contraceptive mindset”… and that is not the teaching of the church. NFP is a gift from God given to couples who have prayerfully considered their fertility as a gift, and are asking God to help them abstain during the fertile phase of the cycle. ABC requires no sacrifice… NFP requires the sacrifice of abstinence.
I hope this helps a bit…