1. All saints, that are united to Jesus Christ their Head, by His Spirit, and by faith, have fellowship with Him in His grace, sufferings, death, resurrection, and glory (1 John 1:3; Eph. 3:16–19; John 1:16; Eph. 2:5–6; Phil. 3:10; Rom. 6:5–6; 2 Tim. 2:12): and, being united to one another in love, they have communion in each other’s gifts and graces (Eph. 4:15–16; 1 Cor. 12:7; 3:21–23; Col. 2:19), and are obliged to the performance of such duties, public and private, as do conduce to their mutual good, both in the inward and outward man (1 Thess. 5:11, 14; Rom. 1:11–12, 14; 1 John 3:16–18; Gal. 6:10).
Referring here to the company of the regenerate (the saints are those united to Christ by the Spirit and by faith), the Westminster theologians make the scriptural point that such regenerate believers have complete fellowship in Christ in all that He has—grace, suffering, etc. As a result of being united to Christ, they are therefore united to one another in love. How could two people both be united to Christ, and not be united to one another? With this union, we are tied together in our gifts and graces. Following this, we are bound in our duties one to another. These duties are both public and private, and pertain to the good of one another, whether external or internal.
2. Saints by profession are bound to maintain an holy fellowship and communion in the worship of God, and in performing such other spiritual services as tend to their mutual edification (Heb. 10:24–25; Acts 2:42, 46; Isa. 2:3; 1 Cor. 11:20); as also in relieving each other in outward things, according to their several abilities and necessities. Which communion, as God offereth opportunity, is to be extended unto all those who, in every place, call upon the name of the Lord Jesus (Acts 2:44–45; 2 Cor. 8; 9; 1 John 3:17; Acts 11:29–30).
At the center of our duties to one another, we find our duty to maintain this union in the worship of God. In other words, the point of unity should be cultivated in order to maintain our unity. If we turn to face one another as the principle of unity, we lose our ability to keep the unity. But unity in worship does not exclude ministering to one another in the necessities of this life—food, shelter, comfort, etc. The only requirements for this communion would be the common faith, and the providential opportunities.
3. This communion which the saints have with Christ, doth not make them in any wise partakers of the substance of His Godhead; or to be equal with Christ in any respect: either of which to affirm is impious and blasphemous (Col. 1:18–19; 1 Cor. 8:6; Isa. 42:8; 1 Tim. 6:15–16; Ps. 45:7; Heb. 1:8–9). Nor doth their communion one with another, as saints, take away, or infringe the title or propriety which each man hath in his goods and possessions (Exod. 20:15; Eph. 4:28; Acts 5:4).
Our communion with Christ is covenantal, and not ontological. If we neglect covenant theology, we get into trouble because the Bible clearly teaches our union with Him. But if there is no such thing as covenant union, then ontological union is the only option left. In the same way, the saints do not become ontologically one with each other, making property and marital relations common. Rather, we are covenantally one with one another, and this means our obligations are limited and defined by covenant.