The Savior said His apostles are not of the world even as He is not of the world. The apostles are a link to Him. Watch them. Listen to them.
At night, the moon reflects the light of the sun to us. When we are not able to see the sun, it’s obvious the moon does. Similarly, we may not be able to see the Son today, but it’s easy to recognize His apostles do. They reflect His light onto us.