The way God's Spirit manifests itself most convincingly is through its fruits: "love, joy, peace, patience, kindness, goodness, trustfulness, gentleness and self-control" (Galatians 5:22). These fruits speak for themselves. It is therefore always better to raise the question "How can I grow in the Spirit?" than the question "How can I make others believe in the Spirit?"
For further reflection...
"My message and my preaching were not with wise and persuasive words, but with a demonstration of the Spirit's power, so that your faith might not rest on human wisdom, but on God's power." - 1 Corinthians 2: 4,5 (NIV)
This devotional was written by Henri Nouwen.
You can find his site here: www.henrinouwen.org