As members of the Catholic Church, we believe in all that has been revealed to us by Our Lord Jesus Christ, whether through Scripture or Tradition. We are committed to fulfilling Our Lord's commands by spreading the Gospel to the whole world, inviting all peoples to receive Our Lord's gift of salvation, both within the Church and outside of her. We do this by gathering as a community for worship through the Holy Mass and regular devotions, through our commitment to social justice, and by living the Gospel values in our daily lives.
Now, this probably needs a lot of work, but I hope this draft can be a starting point for further discussion on a framework on a truly Catholic mission statement. Then again, maybe we can just use Mark 16:15 as mission statement: "Go into all the world and preach the gospel to the whole creation." (RSV:CE)