Look at an electric lamp. If it is on, there is obviously electric power going through the light bulb or it wouldn’t give off light. Because power is going through the lamp, there is illumination. When bulbs are burnt out; they have no light.
Those who make provisions for sin are Christians who give forth no light (that is assuming they have really received Jesus Christ as their Savior). A believer is known by his fruits. A Christian is a communicator of dunamis-God’s power.
Just as when the current effortlessly flows through wires bringing power to an electric lamp and light into a dark room, the Holy Spirit flows through us, and we become lights to the world. “But ye shall receive power, after that the Holy [Spirit] is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.”