When I first served as a deacon in 1971 (Northside Community Chapel, Paterson, NJ), a book that encouraged my ministry and growth was the CRC's Deacons and Evangelism. It was this resource that spurred my thinking that doing mercy and sharing the gospel are inseparable. This became the foundation of my ministry then as a social worker, and continues to this day as a mercy minister. There is no mercy without the gospel.
Because of its impact on me, I recommend this book from Rev. George Stob. I've attached an excerpt from the book to this post.