Intercession For Fellow Believers
That intercession is a great and necessary part of Christian devotion, is very evident from Scripture. The first followers of Christ seem to support all their love, and to maintain all their intercourse and correspondence, by mutual prayers for one another.
St. Paul, whether he writes to churches or particular persons, shows his intercession to be perpetual for them, that they are the constant subject of his prayers. Thus to the Philippians, "I thank my God upon every remembrance of you, always in every prayer of mine for you all making request with joy" (Phil. 1:3-4). Here we see, not only a continual intercession, but performed with so much gladness, as shows that it was an exercise of love in which he highly rejoiced.
His devotion had also the same care for particular persons, as appears by the following passages: "I thank God, whom I serve from my forefathers, with a pure conscience, that without ceasing I have remembrance of thee in my prayers night and day" (2 Tim. 1:3). How holy an acquaintance and friendship was this, how worthy of persons that were raised above the world, and related to one another, as new members of a kingdom of Heaven!
Apostles and great saints did not only thus benefit and bless particular churches, and private persons; but they themselves also received graces from God by the prayers of others. Thus saith St. Paul to the Corinthians: "You also helping together by prayer for us, that for the gift bestowed upon us by the means of many persons, thanks may be given by many on our behalf" (2 Cor. 1:11).
This was the ancient friendship of Christians, uniting and cementing their hearts, not by worldly considerations, or human passions, but by the mutual communication of spiritual blessings, by prayers and thanksgivings to God for one another.
It was this holy intercession that raised Christians to such a state of mutual love, as far exceeded all that had been praised and admired in human friendship. And when the same spirit of intercession is again in the world, when Christianity has the same power over the hearts of people that it then had, this holy friendship will be again in fashion, and Christians will be again the wonder of the world, for that exceeding love which they bear to one another.
For a frequent intercession with God, earnestly beseeching Him to forgive the sins of all mankind, to bless them with His providence, enlighten them with His Spirit, and bring them to everlasting happiness, is the divinest exercise that the heart of man can be engaged in.
Be daily, therefore, on your knees, in a solemn deliberate performance of this devotion, praying for others in such forms, with such length, importunity, and earnestness, as you use for yourself; and you will find all little, ill-natured passions die away, your heart grow great and generous, delighting in the common happiness of others, as you used only to delight in your own.
For he that daily prays to God, that all men may be happy in Heaven, takes the likeliest way to make him wish for, and delight in their happiness on earth.
From A Serious Call To A Devout & Holy Life.