Spiritual power is the divine energy God is willing to express in and through us and the divine authority needed to carry out the work God has called us to do.
We cannot "harness" the power of the Holy Spirit. This power is not just for preachers, evangelists, or people who work in special ministry; rather, it is available to every believer who willingly surrenders moment by moment in submission and obedience to the Holy Spirit.
We cannot garner the power of the Spirit in order to use God. Conversely, we experience His power when we surrender to be used by Him. God releases His power through us as we walk in obedience to Him. Three ways He releases His power to us are:
Through the fruit of the Spirit, God's power and only God's power enables us to exhibit love, joy, peace, patience, goodness, kindness, faithfulness, gentleness, and self-control, which reveal the character of Christ in us.
Through witnessing. Scripture always refers to the power of the Holy Spirit in relationship to witnessing and glorifying God. It is His power through us that emboldens us and carries out the work.
Through the work we are called to do (Zechariah 4:6). God will not place you into a position or ask you to accomplish a task for which He will not fully equip and enable you.