Along with a steady diet of expository Bible preaching and teaching, the central features of Christian catechesis include teaching on the Apostles’ Creed, the Ten Commandments, and the Lord’s Prayer.
The Apostles’ Creed outlines the main elements of Christian faith, the Lord’s Prayer the main elements of Christian hope, and the Ten Commandments the main elements of Christian love. Herman Witsius’ Sacred Dissertations on the Apostles’ Creed (2 vols) provides an excellent overview of the Creed that reflects the best doctrinal and practical instruction of the Reformed tradition.

According to Witsius, the Apostles’ Creed includes three articles, each devoted to one of the three persons of the Trinity, because the Trinity is the “foundations of foundations” upon which all articles of the Christian faith are built.
Not only is the Trinity the “foundation of foundations” for Christian faith. The Trinity is “the principal foundation” of Christian comfort as well. Indeed, Witsius argues, apart from the knowledge of the triune God, the Christian cannot know the comfort of the gospel.
He states:
All the treasures of wisdom and knowledge, are hid in the mystery of God, and of the Father, and of Christ. I cannot know how God can show mercy to a sinner in a manner worthy of himself, unless I know he has a Son whom he could send to make satisfaction for sin, and a Spirit who can apply to me the merits of the Son. If I know not that the Father is God, I shall be ignorant that I am a son of God,–which is the sum of our felicity. If I know not that the Son is God, I shall not form a right estimate of the love of the Father who has given him to me, nor of the grace of the Son, who, though possessing inconceivable majesty, humbled himself so wonderfully for my sake;–nor shall I be able to place a firm dependence upon his satisfaction, which could not be sufficient unless it were of infinite value, or to rely securely on his power, which cannot save me unless it be evidently omnipotent;–it will be impossible for me, in short, to regard him as my Saviour and my Chief Good, because none excepting the true God of Israel is Israel’s God and Redeemer. If, in fine, I am not sure that the Holy Spirit, to whose direction and government I ought to commit myself, is God, I shall not be able to esteem my subjection to him as true liberty, to maintain a holy acquiescence to his protecting care, or to rely on his testimony respecting my salvation as a most ample security. Christian faith is of so delicate a character, that it can firmly acquiesce in none but the Most High God. It must, then, be of the first importance and necessity for us to know a doctrine, on which the knowledge of so many necessary points depends.
Witsius’ two-volume commentary on the Apostles’ Creed belongs in every Reformed pastor’s library because it is a helpful aid in promoting Christian faith and comfort in the triune God, which is our only comfort in life and in death.