Like newborn infants, long for pure spiritual milk, so that through it, you may grow into salvation. (I Peter 2:2)
According to St. Thomas Aquinas, we can understand the invisible work of God in the sacraments by meditating on the visible ways in which we grow, thrive, and recover from injuries physically.
A lot of us, when we think of Holy Baptism, imagine babies at the font. It’s beautiful to think of, but that can get us a little confused between the visible and invisible aspects of this particular meditation. So let’s just think of adults receiving baptism for a second.
The sacrament regenerates us in such a way that we become spiritual babes. Babes in two senses: 1) young, innocent, full of promise and uncorrupted, and 2) needing simple and pure nourishment in order to mature.
A newborn baby at the breast offers us the best possible image, I think, for our souls in their relationship with God and His grace, which He delivers through the solemn works of His Church.
Over time, we grow, strengthen. But we never altogether cease to be babes at the breast, during this pilgrim stage of life.
Yes, Confirmation strengthens us and fulfills Baptism in such a way that confirmed Christians can stand tall, can navigate life as spiritual adults, with heavenly strength and wisdom.
But: we still need breastmilk, too. We still need to rest ourselves on the bosom of the Church. Especially when we fall, and lose a battle with temptation, and need to heal and recover.