Then, again, in c.30 we are told more generally that the prophets were "sent by God through the Holy Spirit."
A fuller treatment is found in several passages. Thus in c.49 we read: "For it is not a man who speaks the prophecies; but the Spirit of God, assimilating and likening Himself to the persons represented, speaks in the prophets and utters the words sometimes from Christ and sometimes from the Father." The thought is found in Justin (Ap.1, 36 ff.), where it is fully dealt with and illustrated by examples.
Again, in c.67: "He took our infirmities," etc. "that is to say, He shall take, etc. For there are passages in which the Spirit of God through the prophets recounts things that are to be as having taken place . . . and the Spirit, regarding and seeing the time in which the issues of the prophecy are fulfilled, utters the words (accordingly)." This again is found in Justin (Dial.114).
In his description of the third point of the Rule of Faith (c.6) he begins with the prophetic function: "The Holy Spirit, through whom the prophets prophesied, and the fathers learned the things of God, and the righteous were led forth into the way of righteousness; and who in the end of the times was poured out in a new way upon mankind in all the earth, renewing man unto God." Here we see the wider conception of the Spirit's work, which marks the advance upon Justin to which we shall refer presently.
So far all has been plain: but, in view of the fact that "the Word of God" is so frequently mentioned in Holy Scripture as coming to the prophets, it was inevitable that difficulty should be felt in distinguishing the functions of the Word and the Spirit in this connection. In c.5 we read, "Now the Spirit shows forth the Word, and therefore the prophets announced the Son of God; and the Word utters the Spirit, and therefore is Himself the announcer of the prophets." A passage in c.73 illustrates this yet further, "David said not this of himself . . . but the Spirit of Christ, who (spake) also in other prophets concerning Him, says here by David: I laid me down and slept: I awoke, for the Lord received me."
A few illustrations may be appended from the five books of the great treatise Against Heresies, II, xli.1: Some Scriptures are too hard for us: "but we know that the Scriptures are perfect, seeing that they are spoken by the Word of God and His Spirit; whereas we are minores et novissimi a verbo dei et spiritu ejus." We are at a great remove from the Word and the Spirit who inspired them. He adds in striking words (§ 3) that "the Scriptures are spiritual: some things we can interpret, others are left with God, and that not only in this world but in that which is to come; that God may for ever be teacher, and man for ever a learner."
Next we may note that Irenæus extends the work of the Holy Spirit to the evangelists: "The Holy Spirit says by Matthew: Now the birth of Christ was on this wise" (III, xvii.1). And a curious collocation is found in III, vi.1: "Neither the Lord nor the Holy Spirit nor the apostles would have definitely called any God, unless He were truly God; nor any Lord save the Ruler of all, the Father, and His Son who received rule from Him." Here perhaps the Holy Spirit is referred to for the Old Testament, the Lord and the apostles for the New. In III, vii.2, however, he recognizes the "impetus" of the Spirit in St Paul's Epistle to the Galatians, especially in his rapid questions and answers: "as though man asked the question, and the Spirit gave the answer."
Enough has been said to show that Irenæus goes beyond Justin's expressions, and widens the function of the Holy Spirit in relation to Scripture. But before we leave the topic we may note that the designation "prophetic Spirit" does occur in Irenæus, only with another or a modified connotation. In III, xi.12 we are told that certain heretics, "in order to frustrate the gift of the Spirit," which in the last days has been poured forth, reject St John's Gospel with its account of the Paraclete: "they reject at once the Gospel and the prophetic Spirit"  ; and, as he says again, "they reject from the Church the grace of prophecy." So also in IV, xxxiv.6: "Some of the prophets beheld the prophetic Spirit and His operations in all manner of charismata" or gifts of grace. The context shows that it is the working of the Spirit in the Christian Church which was foreseen by some of the prophets. We may compare two passages from the end of the Demonstration (cc.99 f.). "Others receive not the gifts of the Holy Spirit, and cast away from themselves the prophetic grace, watered whereby man bears the fruit of life unto God:" and again: "Or else they receive not the Spirit, that is, they reject prophecy."