One of the main themes in the book of Philippians is partnership in the gospel. Beautiful are the feet of those who bring the good news, but blessed are those who send them as well. Those who go and those who send all receive grace from God for the work.
Since cooperation for the gospel is held up as honorable, when should we as a church partner with others? The Baptist Faith and Message has this to say about the topic:
"Christ’s people should, as occasion requires, organize such associations and conventions as may best secure cooperation for the great objects of the Kingdom of God. Such organizations have no authority over one another or over the churches. They are voluntary and advisory bodies designed to elicit, combine, and direct the energies of our people in the most effective manner. Members of New Testament churches should cooperate with one another in carrying forward the missionary, educational, and benevolent ministries for the extension of Christ’s Kingdom. Christian unity in the New Testament sense is spiritual harmony and voluntary cooperation for common ends by various groups of Christ’s people. Cooperation is desirable between the various Christian denominations, when the end to be attained is itself justified, and when such cooperation involves no violation of conscience or compromise of loyalty to Christ and His Word as revealed in the New Testament."
In other words, we should partner together with others whenever it is advantagious to the advance of the gospel and the ministries of the church.
But it is important to think carefully about who we can and should partner with. As Baptists, should we partner with other Baptist churches, even if they're not Southern Baptist? Should we partner with Presbyterians, or Catholics, or Mormons? Should we partner with organizations that are not specifically religious at all, but are focused on meeting needs? Does it change the equation if we are cooperating with someone on an individual level versus on the organizational level? The short answer is that it depends.
Cooperation with other groups depends on what we are partnering together for:
For what could be classified as social issues, such as ending abortion, or fixing the water quality in town, we can partner with just about anyone, so long as we agree with them on the issue. We wouldn't start a teaching ministry with Catholics, but we would stand together agains the issue of abortion.
For good works ministries, such as feeing the hungry or rebuilding houses, our partnerships can stay rather broad as well, teaming up with those who also want to meet these needs. However, it is important to remember in these categories that some partnerships are better than others. Since we believe that no one will be saved apart from hearing the gospel, partnering with needs based ministries who share our desire to spread the gospel would be more desirous than the standard non-religious non-profit.
For Christian schools, we want to consider whether the school belongs to a denomination or is independently run, as well as whether it is incorporating the Christian worldview into all aspects of schooling or is similar to a public school, only with different teachers and a Bible class.
For planting churches or partnering with missionaries, we want to partner with someone that agrees with us on the gospel and on doctrines regarding the church (i.e. first and second tier doctrines).* In other words, if they are planting a church that we would want to attend, then we can and should support them when able.
One truth that Southern Baptists have understood throughout the years is that we are able to accomplish much more together than we can individually. It's what allows our small church to still be involved in sending missionaries and supporting local ministries. And this kind of partnership is what we see modeled for us in the Bible. We must be thoughtful about who we partner with, but we should think of the idea of partnership as a good way to steward what God has given us.
*This idea of first, second, and third tier doctrines comes from the idea of theological triage, written about by Al Mohler here.