Galatians 5:22 is an awkward sentence: “The fruit of the Spirit is…” and then we read nine words. At first glance, it seems that the sentence should read, “The fruits of the Spirit are…” but it doesn’t. The reason is significant.
The sentence is singular because the fruit is singular. The fruit of the Spirit is love—what John Wesley called “the root of all the rest.”  The other eight words are expressions of love…
The phrase “fruit of the Spirit” means that the Spirit makes us what God is, which is love. Inwardly in character and outwardly in conduct we are made to be loving. The Holy Spirit, as the third person of the Trinity, is the mediator of love. Growth in love is what it means to mature. 
We are familiar with the phrase, “You are what you do.” It communicates the truth that our actions pattern us. But there is a deeper truth, “You do what you are.” Our actions emerge from our essence—at least they’re meant to. It is the indwelling Spirit, who is love, who produces the fruit of the fruit of the Spirit, which is love. The Holy Spirit is the spirit of love, and when we are filled with the Spirit, we are filled with live—and thus, most like God. Through the Spirit, the love of the Trinity comes alive in and through us.
 John Wesley, ‘Explanatory Notes Upon the New Testament’ (1755). His comment about Galatians 5:22.
 E. Stanley Jines’ book, ‘Christian Maturity’ (Abingdon Press, 1957) is the best study I know of that connects love and maturity. His book, ‘Growing Spiritually’ (Pierce & Washabaugh, 1953) explores the fruit of the Spirit in depth.