1). For Baptists influenced by the 'New Calvinism', it is helpful to see that for Baptists, Calvinism is not "new". Many Baptists, myself included, embraced Calvinism and became ravenous for the writings of the Reformed tradition. We discovered that past the "5 points", a covenant theology existed, but we assumed it really belonged to the Presbyterians. Yet, if we study our own history, we would see that the large, world-wide Baptist movement across the globe today really came out of a group of solidly Calvinistic, and even covenant theology-holding Particular Baptists. But from the 1800's until the mid 1900's, we lost our Confession. Baptists have a strong, soteriologically rich heritage. If you read the original forward to the confession, the heart of the signatories is oozing with a desire to find common ground with their Presbyterian and Congregationalist brethren. They write in their original letter to the reader, "...contention is most remote from our design in all that we have done in this matter." A helpful history is found here: http://www.
2). It contains a wonderful vision for the Christian life. Early Baptists were convinced of the Ordinary Means Grace. They agreed with their Presbyterian Brethren that the Lord's Supper was more than a memorial. They embraced the God-given rhythm of 1 in 7, and valued Sabbath rest each week. They held that the Moral Law, summarized in the 10 Commandments, while not a means of earning righteousness, was a guide for the believer along the Christian road of joyful obedience. And they valued, with their Protestant counterparts, a strong Word-Centered Christian life.
3). There is value in saying more sometimes. In a day when statements of faith in many churches can be a minimalist endeavor, it is good to have a summarized Systematic Theology. I once heard a dear brother say that the Confession is like a wonderful English garden, where Calvinism is only one set of beautiful flowers contained therein. The early Baptists were not content to have a Calvinistic soteriology alone. They viewed the pieces of systematic theology as fitting together--rising and falling together. If we adopt an historic confession, will this increase our need to disciple new believers, or spend 'extra' time with new church members unfamiliar with a lengthier confession? Yes, but isn't this ultimately a fruitful fulfillment of our commission to make disciples?
4). Historic Confessions ground us. What would Biblical or Systematic or Exegetical Theology be without the aid of Historical Theology? While not inspired Scripture, historic confessions help us to work through doctrine in connection with saints who have gone before us. For Baptists particularly, we have vacillated across a wide expanse of theological understanding since the days of the late 1600's, even since the days of Spurgeon, and this expanse includes several movements that had no real historic connection prior to their sudden development. What if a renewed interest in our own confessional heritage is what we need as we continue to grow and minister for and towards the glory of God?
Consider the 1689. Much more could be said, but Baptists too have their place historically among the Confessional Reformed. I am so thankful for my many Paedobaptist brothers, both awake and asleep, who have guided my theological development in Reformed Theology. I just rejoice that my early Baptist brothers held to it as well...