Short prayer for saying over and over and over again:
Lord, inflame our hearts and our inmost beings with the fire of Your Holy Spirit, that we may serve You with chaste bodies and pure minds. Through Christ our Lord. Amen
A longer prayer to meditate upon:
My God, You have given me a body to keep pure and clean and healthy for Your service and my eternal happiness. Forgive me for all my unfaithfulness in this great responsibility. Forgive me for every mean use which I have made of Your gifts in thought, word or deed since my rebirth as Your own adopted child in Baptism and my registration as a soldier of Jesus on the day of my Confirmation. Create in me a clean heart, O God, and give me a steadfast will that I may be a strength to others around me. Teach me to respect my body and the bodies of my fellow creatures. Help me to see the glory of perfect manhood In Jesus Christ and of perfect womanhood in Mary Immaculate. Inspire me with such love for the ideals for which our Savior lived and died that all my passions and energies will be caught up into the enthusiasm of His service, and evil things will lose their power. May my body be the servant of my soul, and may both body and soul be Your servants. Through Christ our Lord. Amen.
From the Angelic Doctor, St. Thomas Aquinas:
Dearest Jesus! I know well that every perfect gift, and above all others that of chastity, depends upon the most powerful assistance of Your Providence, and that without You a creature can do nothing. Therefore, I pray You to defend, with Your grace, chastity and purity in my soul as well as in my body. And if I have ever received through my senses any impression that could stain my chastity and purity, may You, Who are the Supreme Lord of all my powers, take it from me, that I may with an immaculate heart advance in Your love and service, offering myself chaste all the days of my life on the most pure altar of Your Divinity. Amen
Assisted by Mary and Joseph:
Mary, Mother most pure, and Joseph, chaste guardian of the Virgin, to you I entrust the purity of my soul and body. I beg you to plead with God for me that I may never for the remainder of my life soil my soul by any sin of impurity. I earnestly wish to be pure in thought, word and deed in imitation of your own holy purity. Obtain for me a deep sense of modesty, which will be reflected in my external conduct. Protect my eyes, the windows of my soul, from anything that might dim the luster of a heart that must mirror only Christ-like purity. And when the “Bread of Angels” becomes my food in Holy Communion, seal my heart forever against the suggestions of sinful pleasures. Finally, may I be among the number of those of whom Jesus spoke, “Blessed are the pure of heart for they shall see God.” Amen.
Saint Joseph, father and guardian of virgins, to whose faithful keeping Christ Jesus, innocence itself, and Mary, the virgin of virgins was entrusted, I pray and beseech you by that twofold and most precious charge, by Jesus and Mary, to save me from all uncleanness, to keep my mind untainted, my heart pure, and my body chaste; and to help me always to serve Jesus and Mary in perfect chastity. Amen.