When we go to the Pure Land are we assured that we will attain Buddhahood there?
My answer is yes. But again, there is no way to prove it in rational manners. Ultimately it's all up to our own faith. In this case, the faith in attaining Buddhahood there is based upon the various Mahayana sutras.
I think what is rational is the fact there is no rationality in this world. What we think rational is just "agreement" among our human beings, though it sounds true. However, there will be no proof once we doubt it. On the other hand, once we believe it, anything could be true. The truth is, it's always "hard to believe" and at the same time "easy to doubt."
Master Honen put it simply , " Your own firmly set mind（Ketsujo-shin決定心） creates the conditions for your birth [in the western land (Pure Land)]. If you don't grasp that fact, then your birth is uncertain. If you doubt it, then it's not assured. If you believe your birth to be certain, then it is assured." (Page 17, Words of Dharma / Words of Honen Shonin Chapter 11, Volume 1)
So it's supposed to be very simple. But believing is not that easy. What we need is both wisdom and knowledge. We need a practice just for believing, which I call it "wisdom." And at the same time, we need knowledge. We'd better know what kind of world or realm the Pure Land is. The more we know about pure land, the more we are going to be attracted. If we compare description of the pure land with that of the heaven, pure land is more attractive. Sometimes knowledge alone solve the question. Sometimes knowledge helps the wisdom. So let me write a little knowledge about pure land first.
Generally speaking, the world of pure land is described mainly in the Pure Land Sutras, however, amazing characteristics of Amida's Pure Land were excellently summarized in the collections of "Ojyoyoshu" by Eshin-sozu Genshin (942-1017) in 985. Ojyoyoshu literally means "Essential Collections of the Birth in the Pure Land."
Genshin picked up descriptions of the Amida's Pure Land from different sutras and commentaries from Mahayana Buddhist masters. According to Genshin, 30 merits of the pure land were listed in "Gungiron" and 24 joys were also listed in Ankokusho. Then Genshin listed 10 pleasures of the pure land of Amida Buddha. They are known as "Jodo no Jyu (10) Raku (pleasure)" or 10 pleasures of the pure land which were explained attractively and easily by Genshin.
If we can rely on these knowledge of 10 pleasuers , we can be assured, even now, that we will attain Buddhahood there. 10 pleasures of the pure land are as follows;
1. Shoju Raiko no Raku聖衆来迎の楽 (Pleasure of Amida's Welcome)
At the time of death, Amida Buddha along with Bodhisattvas and Satins, including Kwannon and Seishi, is coming to welcome the Nenbutsu practitioner to his pure land.
2. Renge-shokai no Raku蓮華初開の楽 (Pleasure of the first blossom of the lotus)
At the time of your arrival at pure land, pure and beautiful lotus flower is blooming for you. It is in the lotus flower where you are born in the pure land.
3. Shinso Jinzuu no Raku身相神通の楽 (Pleasure of the amazing characteristics of the body and ability)
Those who attained Ojo have beautiful appearance which is one of the characteristics of Buddha's features. They can have amazing physical visions and hearing so that they know everything in the past and present. They can go anywhere they like.
4. Gomyo Kyogai no Raku 五妙境界の楽 (Pleasure of supreme states of five
According to Mahayana tradition, five senses of human being, to see, to hear, to smell, to taste and to feel, are expressed as Color (to see), Voice( to hear), fragrance( to smell) and flavor (to taste). These five senses will be the supreme ones beyond description in the pure land.
5. Keraku Mutai no Raku 快楽無退の楽 (Pleasure of no recession of pleasures)
Because there is no cause of the suffering, there is nothing but pleasure in the pure land. Pleasures which people enjoy in the pure land is not temporary. They last forever.
6. Injyo Kechien no Raku 引接結縁の楽 (Pleasure of leading people (who are related to you) to the Pure Land)
In this life, we cannot do what we wish to do. Though children want to repay an obligation what they received from parents, but parents cannot always wait (they usually die before children want to take care.) We have so many people that we are indebted. However, the people who are born in the pure land can also have their family and friends to be born there.
7. Shoju kue no Raku聖衆倶会の楽 (Pleasure of meeting Saints who are all Bodhisattvas)
It is written in Amida Kyo. "People who hear about Amida Buddha and his pure land, should wish to be born in the land. Why Because they are able to see all the saints or Bodhisattvas in one place."
The people who are born in the pure land can meet Bodhisattvas and saints , including famous Kwannon and Seishi. People in the pure land can directly prostrate them and also can talk like friends to them.
8. Kenbutsu Monpo no Raku 見仏聞法の楽 (Pleasure of meeting and listening to the Amida Buddha)
In this life, it's very (super) hard to view Amida Buddha. The chance of meeting Buddha's teachings is very rare. Percentage is like there is a wood which has a hole floating in the vast ocean. Then a blind turtle come up to the ocean (*I think once in 100 years) and happen to enter that hole. The chance to meet the Buddha's teaching is very rare like this. Much more difficult to view Buddha in this life. However, the people who are born in the pure land can directly see Amida Buddha and listen to his teachings.
9. Zuishin Kubutsu no Raku随心供仏の楽 (Pleasure of offering directly to Buddha as you wish.)
The people who are born in to the pure land can offer heavenly flower to Amida Buddha six times a day. To not only Amida Buddha, they can also offer flower to various Buddhas anytime as they wish to do.
10. Zoshin Butsudo no Raku 増進仏道の楽 (Pleasure of advancement of the path to the highest enlightenment)
In this life, it's very difficult to get fruits of practice, because there are always obstacles there. Those who are suffering stick to their egos. Those who are enjoying the pleasures, they stick to the pleasures. These egos make it very difficult to walk the path to the enlightenment. But the people who are born in the pure land can walk the path to the highest enlightenment.
Genshin pointed out five reasons that made it possible to achieve the highest enlightenment.
1. Amida Buddha's compassion
2. Amida Buddha's Infinite Light
3. Various sounds in the pure land, such as sounds from birds, wind, and river always preach.
4. No bad reasons and bad friends. Only Bodhisattvas.
5. Eternal life...one can keep practicing toward the practice without having repetition of birth and death.
Now back to the assurance of attaining Buddhahood in the pure land. I think you asked this question not because you want to know my answer but because you want to have "second" to go forward the Nenbutsu path. So I just want to encourage your continued practice.
The wise people tend to reject to have knowledge anymore, which is not wrong. Being wise never mean lots of knowledge. Lots of knowledge never means being wise. However being always open-minded toward the knowledge, we may attain the higher level of wisdom. At the same time, by being mindful of the wisdom, we can accept more knowledge. I think what we need is well-balanced of both knowledge and wisdom. This is exactly like the relationship of "practice" and "faith", if they work together, Ojo (the attainment of the pure land ) will be certain.
I imagine Master Honen would answer your question
like this, " If you believe your attaining Buddhahood in the pure land to be certain, then it is assured. If you doubt it, then it's not
If anyone is interested in Genshin's Ojyoyoshu, there is an English translation online. (I knew it yesterday after translating a part of Ojyoyoshu. How wonderful it's available online! I can save some energy and time when I want to quote Ojyoyoshu in English. Namu Amida Butsu)
There is also a excellent article, The Influence of Genshin's Ojoyoshu on Honen from