10 It is one of the major tenets of Catholic doctrine that man's response to God in faith must be free: no one therefore is to be forced to embrace the Christian faith against his own will. This doctrine is contained in the word of God and it was constantly proclaimed by the Fathers of the Church. The act of faith is of its very nature a free act. Man, redeemed by Christ the Savior and through Christ Jesus called to be God's adopted son, cannot give his adherence to God revealing Himself unless, under the drawing of the Father, he offers to God the reasonable and free submission of faith. It is therefore completely in accord with the nature of faith that in matters religious every manner of coercion on the part of men should be excluded. In consequence, the principle of religious freedom makes no small contribution to the creation of an environment in which men can without hindrance be invited to the Christian faith, embrace it of their own free will, and profess it effectively in their whole manner of life.
Source: Dignitatis Humanae (Vatican.va)