“I will go to the altar of God, to God, the joy of my youth.”
If you are interested in studying to become a priest, feel free to make an appointment with any of the Our Lady of Lourdes priests or with the Springfield Diocese's Vocation Director, Father Brian Alford, at balford@dio.org.
While there are many ways to answer this question, there key differences between religious and diocesan priests are as follows:
Diocesan priests promise obedience to a bishop, and thus are associated with that particular diocese. They live in a parish in their diocese which their bishop assigns them to, or else must be granted permission to serve outside of that diocese. Religious priests, as part of their particular charism, sometimes live in community and serve throughout the world in ministries specified by their religious superiors.
The mission of diocesan priests is parish-based and primarily involves preaching the Gospel, offering the Sacraments, and governing the secular resources of the Church. Religious priests can perform a variety of other ministries, sometimes including but not limited to parish ministry.
Diocesan priests take promises to pray the liturgy of the hours, to obey their bishop and his successors, and to live a life of celibate chastity. Religious priests make vows directly to God to live a life of poverty (meaning that they don't personally own any property), chastity, and obedience (to God, expressed through obedience to their religious superior).
The short answer is that we follow the example of Christ and the Church throughout Her history. During His life, Christ instituted the Sacrament of Holy Orders through 12 men designated as Apostles. Despite His radical inclusion of women into the life of discipleship (uncommon for religions of the time), we find no evidence in the Gospels that Christ instituted women in roles of service to the Church in the same was as He did the Apostles. Likewise, there is no evidence in the Tradition of the Church of ordaining women to the priesthood.
This does not exclude women from a life of service to the Church. Religious life is a beautiful expression of complete dedication and consecration to our Lord, in radical service to Christ and His Church.
Celibacy is the renunciation of marriage made for the sake of a more perfect observance of chastity. Priestly celibacy forgoes the good of sexual partnership in order to more perfectly conform oneself to Christ.
It has been the longstanding tradition of the Church to maintain clerical celibacy among priests. (In certain very specific circumstances, however, a married man may be permitted to be ordained a priest.) This is ultimately to conform to Christ’s own standard to live in celibate chastity for the sake of service to the Kingdom of God, but it also points to the eschatological reality that all of us live for complete and total union with God.
The Sacrament of Holy Orders contains three levels: diaconate, priesthood, and episcopacy. The first level of Holy Orders includes those who desire to be admitted to the priesthood (transitional deacons) and those who are married or celibate who desire to live in permanent service to God and His Church as a deacon (permanent deacons).
Permanent deacons are ordained ministers who help with liturgies, proclaim the Gospel and preach, bury the dead, witness marriages and baptize, and help with the various charitable projects of the Church. Permanent deacons are allowed to be married, but take a promise to remain celibate for the sake of the Church should their spouse die.