Ichinen sanzen means three thousand worlds in a single moment of life.

Not somewhere in the distance. Not in a future state. In this moment, the one you are in right now, with whatever is happening in it.

Nichiren Daishonin identified this as the doctrinal foundation of why chanting Namu Myoho Renge Kyo works. The Kanjin-no Honzon-shō states it plainly: Śākyamuni's causal practices and resulting virtues are all contained within the five characters Myōhō Renge Kyō. When you embrace them, he will naturally transfer to us the merit of his causes and effects.

The transfer is natural. It does not wait for you to understand the structure of ichinen sanzen before it takes effect.

We built a doctrinal guide around that single claim, seven chapters, primary sources only, disputed attributions named directly where they exist.

https://nmrkob.com/products/one-moment-contains-everything-a-practitioners-guide-to-ichinen-sanzen

Vow Keeper members receive it at no cost: https://nmrkob.com/products/one-moment-contains-everything-a-practitioners-guide-to-ichinen-sanzen-2

Namu Myoho Renge Kyo.