The power of the Holy Spirit is not just for salvation, but transformation, a process that might be slow and gradual. The difference might look like this:
I can take ten gallons of gasoline and release a tremendous amount of power and energy by just dropping a lighted match into it. It makes a dramatic onetime impact. But there is another way to release the energy in that gasoline.
I could place it in the fuel tank of a new car, designed to get 30 miles to the gallon. The high tech engine will use that ten gallons of gasoline to take a me 300 miles or more. Explosions may be spectacular, but the sustained, controlled burn has staying power.
"But you shall receive power when the Holy Spirit has come upon you; and you shall be witnesses to Me in Jerusalem, and in all Judea and Samaria, and to the end of the earth.” Acts 1:8 (NKJV)
I don't want to be a flash in the pan, I want to make a difference in this world over time. I want to last for the long haul. The Holy Spirit continues to work in each of our lives day after day. God's not finished with us yet, and that fact should give us great comfort on days when it seems like we should be farther along spiritually than we are.