Objection 1. It seems that before sin sacraments were necessary to man. For, as stated above (1, ad 2) man needs sacraments that he may obtain grace. But man needed grace even in the state of innocence, as we stated in I, 95, 4 (cf. I-II, 109, 2; I-II, 114, 2). Therefore sacraments were necessary in that state also.
Objection 2. Further, sacraments are suitable to man by reason of the conditions of human nature, as stated above (Article 1). But man's nature is the same before and after sin. Therefore it seems that before sin, man needed the sacraments.
Objection 3. Further, matrimony is a sacrament, according to Ephesians 5:32: "This is a great sacrament; but I speak in Christ and in the Church." But matrimony was instituted before sin, as may be seen in Genesis 2. Therefore sacraments were necessary to man before sin.
On the contrary, None but the sick need remedies, according to Matthew 9:12: "They that are in health need not a physician." Now the sacraments are spiritual remedies for the healing of wounds inflicted by sin. Therefore they were not necessary before sin.
I answer that, Sacraments were not necessary in the state of innocence. This can be proved from the rectitude of that state, in which the higher (parts of man) ruled the lower, and nowise depended on them: for just as the mind was subject to God, so were the lower powers of the soul subject to the mind, and the body to the soul. And it would be contrary to this order if the soul were perfected either in knowledge or in grace, by anything corporeal; which happens in the sacraments. Therefore in the state of innocence man needed no sacraments, whether as remedies against sin or as means of perfecting the soul.
Reply to Objection 1. In the state of innocence man needed grace: not so that he needed to obtain grace by means of sensible signs, but in a spiritual and invisible manner.
Reply to Objection 2. Man's nature is the same before and after sin, but the state of his nature is not the same. Because after sin, the soul, even in its higher part, needs to receive something from corporeal things in order that it may be perfected: whereas man had no need of this in that state.
Reply to Objection 3. Matrimony was instituted in the state of innocence, not as a sacrament, but as a function of nature. Consequently, however, it foreshadowed something in relation to Christ and the Church: just as everything else foreshadowed Christ.
Source: Summa Theologica (New Advent)