The Universal church is that general church of the whole congregation of the called-out believers, that make up of the Body of Christ, “The People of God.” as opposed to the local church, a congregation of believers meeting together for fellowship at a particular locale having a set of agreed beliefs and dogmas.
There are several forms the unity of the church can take even though generally unity of the universal church is desired and agreed. Four common forms are practiced; the first being “Mutual Recognition and Fellowship.” This is the most basic low-level of unity, recognizing each other as legitimate parts of the family of God, cooperating whenever in evangelistic crusades and fellowshipping whenever possible on an ad hoc basis.
The second level is “Conciliar Unity” when churches have organizational alliances to achieve their common purposes. They band together into council or association of churches. This is basically a cooperative fellowship while each church still retains its own identity. The unity is visible as well as spiritual.
The final type of unity is “Organic Unity” in which there is an actual creation of one organization in which separate identities are surrendered. Membership and ordination are joined.
I think the best form of unity that is Biblical is the “Conciliar Unity” as the Bible allows for variety as long as they stay with the Bible. The different denominations do not feel threaten when coming together to fellowship and cooperate in evangelistic efforts, fulfilling the functions of the church.