The Heidelberg Catechism explicitly adopts a threefold structure in its treatment of Christian doctrine.
Question 2. How many things are necessary for thee to know, that thou, enjoying this comfort, mayest live and die happily?
Answer: Three; the first, how great my sins and miseries are; the second, how I may be delivered from all my sins and miseries; the third, how I shall express my gratitude to God for such deliverance.
Francis Turretin demonstrates the benefits of knowing those three things, and finds them exhibited in the OT ceremonial law:
With regard to the covenant of grace, there was a use of the law to show its necessity by a demonstration of sin and of human misery; of its truth and excellence by a shadowing forth of Christ and his offices and benefits; to seal his manifold grace in its figures and sacraments; to keep up the expectation and desire of him by that laborious worship and by the severity of its discipline to compel them to seek him; and to exhibit the righteousness and image of the spiritual worship required by him in that covenant. Undoubtedly three things are always to be specially inculcated upon man: (1) his misery; (2) God’s mercy; (3) the duty of gratitude: what he is by nature; what he has received by grace; and what he owes by obedience. These three things the ceremonial law set before the eyes of the Israelites, since ceremonies included especially these three relations. The first inasmuch as they were appendices of the law and the two others as sacraments of evangelical grace. (a) There were confessions of sins, of human misery and of guilt contracted by sin (Col. 2:14; Heb.10:1-3). (b) Symbols and shadows of God’s mercy and of the grace to be bestowed by Christ (Col. 2:17; Heb. 9:13,14). (c) Images and pictures of duty and of the worship to be paid to God in testimony of a grateful mind (Rom. 12:1). Misery engendered in their minds humility; mercy, solace; and the duty of gratitude, sanctification. These three were expressly designated in the sacrifices. For as they were a “handwriting” on the part of God (Col. 2:14) representing the debt contracted by sin, so they were a shadow of the ransom (lytrou) to be paid by Christ (Col. 2:17, Heb. 10:5,10) and pictures of the reasonable (latreias logik?s) and gospel worship to be given to God by believers (Rom. 12:1; 1 Pet. 2:5)
(Institutes of Elenctic Theology XI,24.9, punctuation slightly modified for clarity)