A. Let us first read the quote from the short Upaddha Sutta found in the Samyutta Nikaya XLV.2, which I think you are quoting.

…Ananda approached the Buddha, paid homage, sat down to one side, and said, ‘Lord, this is half of the holy life, that is, good friendship, good companionship. Good comradeship.’
‘Not so, Ananda! Not so, Ananda!’ replied the Buddha, ‘This is the entire holy life, Ananda, that is, good friendship, good companionship, good comradeship. When a bhikkhu has a good friend, a good companion, a good comrade, it is to be expected that he will develop and cultivate the Noble Eightfold Path’…

To my way of thinking there are two key words here, ‘holy’ and ‘expected’, which we need to explore so as to better understand the meaning of this Sutta.

I was a Theravada monk for a few years and I often heard that being a monk was to lead the holy life. But how exactly was this defined? To many, simply to don the saffron robes was enough to fulfil that ideal, but to most monks it meant a whole lot more.

There are around 250 rules for monks to follow coupled with countless minor ‘rules’ that help them not only to stay within the main body of rules but refine still further the very basis of the monastic life, which is to nurture detachment from our tendency to grasp at life. These are the many little pointers that encourage the monk to build an optimum state of being, an optimum state of consciousness conducive to the unfolding of insight. This very refined way of living cannot successfully be put in place when pursued alone, if for no other reason than much of what they need to refine involves interaction and consideration for their fellow bhikkhus and community. Having a ‘good friend’, being given support, consideration and kindness, as well as being inspired by their company and exemplary conduct, becomes the bedrock of the ‘holy life’.

From this platform the monk is then expected to develop and cultivate the noble eightfold path. That is, practise the complete Dharma path. Apparently two separate pursuits?Possibly so. They can be separated. A monk can just pursue the holy life and become a good respectful person with high ethical standards as well as being kind and helpful. But another whilst pursuing the holy life can move more deeply into the practice of the eightfold path.

I have met and have known fine monks that many would consider without hesitation to be leading the ‘holy life’, who have had no inclination to practise the whole of the eightfold path at all. Sila yes, but that is all. Fine, ethical, kind beings that may study and preach and do fine work in their community and temple, but have never pursued meditation and the cultivation of wisdom into the reality of their own being. So leading the ‘holy life’ and being a ‘good friend’ cannot be seen as the complete picture of a spiritual pursuit.

Footnote. Remember: Most of what you read in the Pali Canon is for the ordained monk. The so-called ‘holy life’ is letting you know that it is not possible for a layman to cultivate some of the more refined aspects of Buddhist practice. In my Theravada days I often heard this expression ‘holy life’ used to let the congregation know, in a somewhat coded way, that there is a definite (superior) space between the ordained and the lay, so we should always remember that. Assertions like this convinced me of my love for Mahayana, where no such distinctions exist.

To answer your last question: You are suggesting this Sutta could be a way of expounding ‘spiritual friendship’. I think you can do this to a degree as long as you realise that a friendship that is ‘spiritual’ is not the same as any other type of friendship. Other friendships, however sincere and skilful, nearly always carry attachments that by nature will have self-interest and are karma producing – even if we consider our actions towards such friends as being ‘selfless’. Genuine spiritual friendship has non-attachment as its main characteristic – to help your friend without self-interest and attachments. A very difficult ideal to pursue and perfect, and quite impossible without a mature practice of the eightfold path in place. This then may imply more of a teacher/student relationship, and I don’t think this is the teaching of this Sutta. In fact, from my understanding of my days in Theravada the authentic ‘spiritual friend’ could only be either the Buddha or one of the arhats, as these are the only beings whose training has finished and are therefore qualified to teach.