In the Beginning
The family is the very core of Creation. In the beginning, the LORD, Our Father, spoke the words of creation, which were sent forth by the Spirit, the Holy Spouse, in order to bring forth life. All creatures were brought forth into families--male and female together for the propagation and rearing of offspring. God's crowning jewel of Creation was the first family, Adam and Eve who were instructed to go forth and multiply and fill the earth with their children. Family is the heart of all that we believe, so it is no wonder that every vocation is rooted in the context of family.
When we speak of raising our children for vocation, most often that implies the holy vocations of the priesthood, and holy sisters and brothers. However, every child is created and called for a specific vocation. Every child is sent forth by the Father to construct a family in this world and to lead that family into the Heavenly realms of the next.
Marriage was the first vocation instituted by God. Adam and Eve were given to each other in service and love for the purpose of producing offspring for the LORD. There were no priests before the Fall, for the LORD God walked throughout the Garden of Eden. Man for the first and last time since the dawn of time, could freely meet with God face to face. Adam and Eve's purpose was not only to serve each other, but to lead each other in praise and obedience to God. Their children were meant to be raised up for Heaven and to spread the perfect Love of the Father to the ends of the earth. However, instead they were tempted, turned from God to self, and were forever banished from paradise. Marriage is still a holy and worthy vocation, it is necessary for the Church here on earth to continue and for saints to be brought forth to guide us in this journey, and then stand with the LORD in Heaven.
Once man was cast out and stained with sin, the doors of Heaven were locked and the face of God concealed. Thus, the vocation of the priesthood arose. Priests in the Old Covenant were the people's one link to God, their only means of communicating with their Creator. Priests now are ministers of the mercy and grace of Christ, who celebrate the ultimate sacrifice each day for the Church, the Body of Christ, the family of the Living God. Priests are wed to the Holy Mother Church. Their vocation is to bring forth spiritual children and raise them up for the Kingdom, teaching them to serve God and man. Priests must sacrifice, just as any spouse does, their will for the good of the other. They must be fruitful and multiply in spiritual terms, shepherding their flock. This is why they are called "father."