Beltane

Quite obviously, this song is about the Celtic holiday of Beltane. AKA May Day. In their tradition, May Day was the start of the new year, hence "Have you ever stood in the April wood and called the new year in?"
It's the end of April, and they are ready to call in the new year on Beltane. This song is so joyful, and come next Beltane... This song will be playing at my party :D

Here are more complete lyrics:

"Beltane"

Have you ever stood in the April wood and called the new year in? While the phantoms of three thousand years fly as the dead leaves spin? There's a snap in the grass behind your feet and a tap upon your shoulder. And the thin wind crawls along your neck it's just the old gods getting older. And the kestral drops like a fall of shot and the red cloud hanging high come a Beltane. Have you ever loved a lover of the old elastic truth? And doted on the daughter in the ministry of youth? Thrust your head between the breasts of the fertile innocent. And taken up the cause of love, for the sake of argument. Or while the kisses drop like a fall of shot from soft lips in the rain come a Beltane. Happy old new year to you and yours. The sun's up for one more day, to be sure. Play it out gladly, for your card's marked again.

Have you walked around your parks and towns so knife-edged orderly? While the fires are burned on the hills upturned in far-off wild country. And felt the chill on your window-sill as the green man comes around. With his walking cane of sweet hazel brings it crashing down. Sends your knuckles white as the thin stick bites. Well, it's just your groaning pains. Come a Beltane. Come a Beltane. Come a Beltane. Come a Beltane. Come a Beltane. Come a Beltane. Come a Beltane. Come a Beltane.