Every good gift and every perfect gift is from above, and comes down from the Father of lights, with whom there is no variation or shadow of turning.
James 1 :17
In my Girl Scouting days, I'd sit around at night in a tent, gathered with other girls around an oil lamp while we played cards or strummed guitars. The lamplight cast shadows on the tent canvas as the light danced and turned. The flickering light had its own beauty, but its shadows revealed its imperfections. The light was dim here and brighter there. The slightest obstacle, such as the wire handle of the lamp, was enough to block the light and cast a shadow. If someone picked up that lamp or turned it a bit, the shadows would twirl above our heads.
This verse compares God to a light in which there is no variation or shadow of turning. It is light in all its perfection. No obstacle blocks its advance. There is no flicker due to dimness or variation. No shadow in the turning. Perfect, unflinching, brilliant light. Perfect in holiness and goodness. A light we of this world have never seen, but can only imagine.
The context of this verse is not being tempted through trials, but being obedient to God through them. It is not God who tempts us, James tells us, but we are tempted by our own evil desires. Just about the time I think I'm strong enough to endure trials rather well, God sends another one, a different one, and I fall short again and I'm humbled. This, too, is a good and perfect gift from the Father of lights. Just the gift I needed at such a time as this.