The cause of the perversion by Protestants of the traditional concept of communion of saints is not to be found in the alleged lack of Scriptural and early Christian evidence in favour of that concept; well-informed Protestant writers have long since ceased to press that argument. Nor is there any force in the oft-repeated argument that the Catholic dogma detracts from Christ’s mediatorship, for it is plain, as St. Thomas had already shown (Suppl., 72:2, ad 1), that the ministerial mediatorship of the saints does not detract from, but only enhances, the magisterial mediatorship of Christ. Some writers have traced that perversion to the Protestant concept of the Church as an aggregation of souls and a multitude of units bound together by a community of faith and pursuit and by the ties of Christian sympathy, but in no way organized or interdependent as members of the same body. This explanation is defective because the Protestant concept of the Church is a fact parallel to, but in no way causative of, their view of the communion of saints. The true cause must be found elsewhere. As early as 1519, Luther, the better to defend his condemned theses on the papacy, used the clause of the Creed to show that the communion of saints, and not the papacy, was the Church: “non ut aligui somniant, credo ecclesiam esse praelatum . . . sed . . . communionem sanctorum”. This was simply playing on the words of the Symbol. At that time Luther still held the traditional communion of saints, little dreaming that he would one day give it up. But he did give it up when he formulated his theory on justification. The substitution of the Protestant motto, “Christ for all and each one for himself”. In place of the old axiom of Hugh of St. Victor, “Singula sint omnium et omina singulorum” (each for all and all for each–P.L., CLXXV. 416), is a logical outcome of their concept of justification; not an interior renovation of the soul, nor a veritable regeneration from a common Father, the second Adam, nor yet an incorporation with Christ, the head of the mystical body, but an essentially individualistic act of fiducial faith. In such a theology there is obviously no room for that reciprocal action of the saints, that corporate circulation of spiritual blessings through the members of the same family, that domesticity and saintly citizenship which lies at the very core of the Catholic communion of saints. Justification and the communion of saints go hand in hand. The efforts which are being made towards reviving in Protestantism the old and still cherished dogma of the communion of saints must remain futile unless the true doctrine of justification be also restored.
Consequently, it’s not much of a stretch to think that between their overwhelming love for God and their experience of being perpetually in God’s presence, that their prayers are consequently more likely to be effective than those of any of the aforementioned people, and consequently, are marvelous friends to have on your side. 
S 1305.