Why does the Creed say “he rose again the third day, according to the Scriptures?”
The Creed is founded on the Holy Scriptures, and these words come directly from the Apostle: “For I delivered to you, first of all, what I also received: that Christ died for our sins according to the Scriptures, that he was buried, that he was raised on the third day according to the Scriptures” (1Co 15:3–4; see Q017, Q203). This appeal to the testimony of the Scriptures was taught by Christ himself: “Have you not read what was spoken to you by God?” (Mat 22:31; see Q057); “Search the Scriptures, for you think that in them you have eternal life; and it is they that bear witness to me” (Joh 5:39; see Q032); “Scripture cannot be broken” (Joh 10:35; see Q057).
In the context of St Paul’s formula, they show that Jesus Christ died and rose again precisely as had been written of him prophetically in the books of the Old Testament, the resurrection is not an isolated wonder, but the fulfillment of the whole economy of revelation (cf. Luk 24:25–27, 44–46; see Q192).
More generally, this statement underlines the importance of the Holy Scriptures in the life of a Christian within the life of the Church. As St Innocent writes:
First of all, a Christian must thoroughly study the foundations of the Christian faith. To that end, you must read and reread the Holy Scriptures on a regular basis, especially the books of the New Testament… learning not only their contents but also their origin: who wrote them and when, how they have been preserved and handed down to us, and why they are called divine and sacred… In addition to the Scriptures, it is useful to become familiar with the works of the Church Fathers… which will help you comprehend your faith more deeply… When you become convinced that our Orthodox faith is founded on the Holy Scriptures, and that they contain the true word of God revealed by the Holy Spirit through prophets and apostles, accept it with all your trusting heart (St Innocent of Alaska, Indication of the Way into the Kingdom of Heaven; see section on Scripture within Tradition).
In the fifty-third chapter of Isaiah, the suffering and death of Jesus Christ are announced in exact detail: “He was wounded for our transgressions, he was bruised for our iniquities; the chastisement of our peace was upon him, and with his stripes we are healed” (Isa 53:5; see Q192). Concerning the resurrection, the Apostle Peter, on the day of Pentecost, quotes the sixteenth Psalm: “You will not abandon my soul to Hades, nor allow your Holy One to see corruption” (Psa 16:10 [15:10 LXX]; Act 2:25–31), arguing that David, who died and was buried, spoke prophetically of the resurrection of the Christ.