Creeds, confessions and statements of faith have always been an important part of the expression of the Reformed faith. Along with classic creeds, such as the Apostle's Creed and Nicene Creed, the written statements of the church of the Reformation grew with the work of Calvin, with his Institutes, and Zwingli, with his Sixty-Seven Articles. During this early time of the Reformed faith, many confessions were written: the Helvetic Confessions, the Confession of Geneva. the Scots Confession the Belgic Confession, and the Westminster Confession, among others. Another form of religious expression was the catechism, such as the Heidelberg and the Westminster catechisms. Many Reformed denominations claim to believe in the Three Forms of Unity, which are the Belgic Confession, the Heidelberg Catechism and Canons of Dort. More recent expressions of faith in the Presbyterian Church have been the Confession of 1967, centered around the doctrine of reconciliation, and the "Brief Statement of Faith", on the occasion of the union of two Presbyterian denominations.