When I write about the Wesleys, I do so from within the tradition which has most substantially shaped my Christian faith. Fortunately, the Wesleyan tradition is ecumenical, itself the child of other streams of Christianity, and one which invites us to be formed in relation to the depth and breadth of Christian thought. All this to say, the theology of love found in the Wesleyan tradition is the culmination of previous theologies in the Roman, Orthodox, Protestant, and Anglican traditions.
In addition to the breadth of its theology of love, we also find a depth such that many rightly describe Wesleyan theology as a theology of love.  In demonstrable ways we see this.
First, with respect to theology itself. The fact that neither John nor Charles Wesley spent their lives in the academy has caused some to discount them as theologians, but that is a both a bogus claim, and one which reveals a too narrowing of the word ‘theologian.’ Their media were different (e.g. sermons, hymns, treatises, and letters) but their message has theological substance. And their message was rooted in the two great commandment—the love of God and neighbor. Writing sixty years ago, Colin Williams confirmed John Wesley’s alignment with and commitment to the universal Christian belief that faith is formed by love. 
Second, love is seen with respect to the ministries that characterized Methodism. One of the guiding mantras for John and Charles (and other Methodists) was “faith working by love,” a conviction akin to St. James, who wrote that “ faith is dead when it does not arise from faithful activity” (James 2:17). John Wesley called it “practical divinity,”—what he (and the larger Christian tradition) referred to as social holiness.
My study of Wesleyan spirituality has shown how much John and Charles (and the Methodist movement) connected with, benefitted from, and expressed the many theologies of love which preceded them.  I have come to believe that they saw Methodism as a Third Order, akin to what we have seen in the Franciscan order–a movement rooted in and expressive of love.
Love as the cornerstone of faith and life has generated this principle throughout the Wesleyan world, “Methodists move toward people who need help.”  The help given is not generated solely or primarily by a sense of obligation or duty, but rather from compassion born of love—a sense of love rooted in the person and work of God, who in the Holy Trinity loves the whole world (John 3:16).
 Nazarene theologian Mildred Bangs Wynkoop left no doubt as to her recognition of this, entitling her study of Wesleyan theology, ‘A Theology of Love’ (Beacon Hill Press, 1972).
 Colin W. Williams, ‘John Wesley’s Theology Today’ (Abingdon Press, 1960), 65.
 My PhD dissertation launched my study of Wesleyan spirituality: ‘The Devotional Life of John Wesley: 1703-38’ (Duke University, 1981). I have since written about this in books and articles–for example, ‘Devotional Life in the Wesleyan Tradition’ (Upper Room Books–first as a book in 1983, and then republished as a workbook in 1996). The workbook is still in print.
 A statement made by Nazarene theologian J. Kenneth Grider in an unpublished paper he wrote in 1999.