“fundamentum fidei: foundation of faith i.e., Christ, on whom the faith and salvation of humanity rests.
Richard Muller, Dictionary of Latin and Greek Theological Terms: Drawn Principally From Protestant Scholasticism, fundamentum fidei.
The foundation of faith can be divided into three parts:
“(1) the fundamentum substantiale, or substantial foundation, in Christ, the substance and object of faith.”
Muller, Dictionary, fundamentum fidei.
“(2) the fundamentum organicum, the organic or instrumental foundation, is the Word of God, the principium, or principle of faith, and the chief means of faith.”
Muller, Dictionary, fundamentum fidei.
“(3) the fundamentum dogmaticum, or dogmatic foundation, is that basic teaching of the church that comprises the essential articuli fundamentalies fidei and sustains the faith of the individual Christian.”
Muller, Dictionary, fundamentum fidei.
In sum, the foundation of faith is composed of the incarnate Word of God, the written word of God, and the preached word of God.
Standard Sacred Text.com 