John was filled with the Holy Spirit from his mother's womb according to the promise of the angel.  We should not be surprised that John grew "strong in spirit." Since it is not possible from the Greek manuscripts to determine whether the "s" in spirit should be lower case or upper case, the matter can be debated. In either case, the truth is that the Holy Spirit filled John's spirit and empowered his life. John was not shaped by the culture of the city or by the ways of the Temple. John was shaped by God by living in the same way that God used to shape the people of Israel before they reached the Promised Land — by living in the wilderness.  John's role was unique; his ways were strange and bizarre to us who live many years later. The point Luke wants us to know, however, is that John was Spirit-led. His work set the stage for the dawning of the age of the Holy Spirit and the New Covenant.  That Spirit is ours when we become Christians. He leads, guides, transforms, equips, and informs us as the children of God and helps us be all that we can be. We, too, can become strong in the Spirit!
Father, I know that your Son poured out the Holy Spirit upon me when I became a Christian. I know your Spirit lives in me and makes my body a holy temple where you live. So I ask that you make me strong in the Spirit. May your will and your character take shape in my life as the Holy Spirit has more influence and control of my will. In Jesus' name. Amen.