It is this close union which the Apostle here indicates as being the foundation and the source of all that gladness which he desires to see spreading its light over the Christian life. 'Rejoice in the Lord'--being in Him be glad.
Now that great thought has two aspects, one deep and mysterious, one very plain and practical. As to the former, I need not spend much time upon it. We believe, I suppose, in the superhuman character and nature of Jesus Christ. We believe in His divinity. We can therefore believe reasonably in the possibility of a union between Him and us, transcending all the forms of human association, and being really like that which the creature holds to its Creator in regard to its physical being. 'In him we live, and move, and have our being' is the very foundation truth in regard to the constitution of the universe. 'In Him we live, and move, and have our being' is the very foundation truth in regard to the relation of the Christian soul to Jesus Christ. All earthly unions are but poor adumbrations from afar of that deep, transcendent, mysterious, but most real union, by which the Christian soul is in Christ, as the branch is in the vine, the member in the body, the planet in its atmosphere, and by which Christ is in the Christian soul as the life sap is in every twig, as the mysterious vital power is in every member. Thus abiding in Him, in a manner which admits of no parallel nor of any doubt, we may, and we shall, be glad.
But then, passing from the mysterious, we come to the plain. To be 'in Christ' which is commended to us here as the basis of all true blessedness, means that the whole of our nature shall be occupied with, and fastened upon, Him; thought turning to Him, the tendrils of the heart clinging and creeping around Him, the will submitting itself in glad obedience to His beloved and supreme commandments, the aspirations, and desires feeling out after Him as the sufficient and eternal good, and all the current of our being setting towards Him in earnestness of desire, and resting in Him in tranquillity of possession. Thus 'in Christ' we may all be.
And, says Paul, in the great words of my text, such a union, reciprocal and close, is the secret of all blessedness. If thus we are wedded to that Lord, and His life is in us and ours enclosed in Him, then there is such correspondence between our necessities and our supplies as that there is no room for aching emptiness; no gnawing of unsatisfied longings, but the blessedness that comes from having found that which we seek, and in the finding being stimulated to a still closer, happier, and not restless search after fuller possession. The man that knows where to get anything and everything that he needs, and to whom desires are but the prophets of instantaneous fruition; surely that man has in his possession the talismanic secret of perpetual gladness. They who thus dwell in Christ by faith, love, obedience, imitation, aspiration, and enjoyment, are like men housed in some strong fortress, who can look out over all the fields alive with enemies, and feel that they are safe. They who thus dwell in Christ gain command over themselves; and because they can bridle passions, and subdue hot and impossible desires, and keep themselves well in hand, have stanched one chief source of unrest and sadness, and have opened one pure and sparkling fountain of unfailing gladness. To rule myself because Christ rules me is no small part of the secret of blessedness. And they who thus dwell in Christ have the purest joy, the joy of self-forgetfulness. He that is absorbed in a great cause; he whose pitiful, personal individuality has passed out of his sight; he who is swallowed up by devotion to another, by aspiration after 'something afar from the sphere of our sorrow,' has found the secret of gladness. And the man who thus can say, 'I live: yet not I, but Christ liveth in me,' this is the man who will ever rejoice. The world may not call such a temper gladness. It is as unlike the sputtering, flaring, foul-smelling joys which it prizes--like those filthy but bright 'Lucigens' that they do night work by in great factories--it is as unlike the joy of the world as these are to the calm, pure moonlight which they insult. The one is of heaven, and the other is the foul product of earth, and smokes to extinction swiftly.