If religious art symbolizes the appeal of Venice, then the Venice Biennale has come to symbolize how contemporary art has become a new and increasingly popular religion.

Over 370,000 visitors a year come to engage with the latest ideas; to criticize perhaps, but mostly to imbibe and learn.

To be selected to show here is the highest sign of approval for both young and established artists, and the ultimate accolade for the curator who devises the central exhibition.

The first African curator

This year, the central official exhibition is curated by Nigeria's Okwui Enwezor, the first African curator to have that honor, and he sets an overtly political agenda.

Diversity is one of the key words and he has made a point of inviting artists from all over the post-colonial world who may have been excluded from previously western centric processes of selection and represent different views of the world, or simply living in the West, some of whom (Chris Ofili, Glen Ligon) have been quite successful.

Economics is another thread. At the entrance, a soundtrack plays with actors reading from Karl Marx's Das Kapital.

Enwezor believes that Marx's central thesis concerning the value of money and the exploitation of labor is still crucially relevant today and that artists should consider the precarious situation of global unrest -- and economic and social insecurity -- we are in.

Human rights take center stage

Just where his exhibition meets the waterfront are two 100-foot, 8-ton sculptures of winged creatures (Phoenixes) made from discarded construction tools by Chinese artist, Xu Bing, in protest at the conditions laborers worked under during the construction of the World Financial Center in Beijing.

Such concerns with human rights and oppression spill out into the 89 National Pavilions dotted around the Giardini, the Arsenale and other locations.

The Iraq pavilion reflects on the terror subjects have suffered at the hands of Islamic State. The Armenian pavilion marks the 100th anniversary of mass killings of Armenians by Ottoman Turks during the First World War.

In a small church, American artist Patricia Cronin had lain piles of discarded young girls' clothes on three altars in memory of girls who have been raped, kidnapped or put into forced labor institutions.

Religion is never far from the surface, and pavilions have been at pains to cross boundaries.

Iceland, for example, commissioned Swiss artist Christoph Buchel to turn a disused Catholic church into the first Islamic mosque ever seen in Venice, much to the alarm of Italian police who are considering it a security risk.

A better life through mushrooms

One of least promoted events was also one of the most interesting. If diversity is a theme of this year's Biennale, Belgian artist, Koen Vanmechelen's is more specifically bio-diversity with a humanitarian purpose.

He shipped a dromedary camel down the Grand Canal and out to a breeding center on the island of Murano, where he is developing super nutritional mushrooms grown on camel and rare black chicken faeces that could enhance human immunity to disease.

The process is accompanied by an apothecary style installation in the Franchetti Palace in Venice -- where assorted contemporary works using glass are being shown -- and a display of Vanmechelen's marketable sculptures and drawings of hybrid creatures in Murano.

The sale of these (priced between 35,000 and 150,000 euros, or $39,000 to $167,000) will help to finance the ongoing project in Belgium.

During the preview, guests were shipped from the Franchetti Palace to Murano where they ate a five course meal that included the mushrooms and all have lived to tell the tale.

The Guggenheim protests

On the way out to Murano Island we saw protestors clambering outside the Peggy Guggenheim collection with a banner that read 'Meet workers' demands.'

This was the Gulf Labour Group voicing their discontent with the conditions migrant laborers to the UAE have been working under, particularly pointed at the Saadiyat Islands off Abu Dhabi where an outpost of the Guggenheim museum is being built. Later the same day, Ukranian artists occupied the Russian pavilion.

But with all the agitprop and political issues that attracted journalistic attention, where was art and beauty? Was the overall tone too didactic to allow for such old fashioned aesthetic pleasures?

A standout among the national pavilions in this sense was the Japanese one with its spectacular, all-embracing installation of hanging nets and falling keys, bathed in crimson and symbolizing the inability of memory to hold onto everything; and the American pavilion with its air conditioned rooms screening video artist Joan Jonas's fanciful narrative of children playing in idyllic landscapes.

The art of proportion

Tackling one of the essential principles of beauty was Dutch dealer Axel Verwoordt in the Palace Fortuny, where went his own way completely and mounted an extensive exhibition on three floors called Proportio Proportio that explored the idea of proportion in art across the centuries.

In one corner an ancient Roman stone figure snuggled up to an old master painting of a classical building, which in turns is overlooked by a much bigger and more colorful geometrical painting by Ellsworth Kelly.

In a small room, thin colored floor to ceiling bars by Fred Sandback are hung with a simple minimal painting in two colors by Brice Marden.

Verwoordt's abilities to mix and match are well known. As expected, the artist he has been most successful with recently -- the Japanese action painter Kazuo Shiraga, whose prices have gone from tens of thousands to millions in the last five years -- featured with a characteristic abstract whirl of paint, though what particular type of proportion this illustrates was unclear. It was a dealer's show after all.

Why so serious?

Laughter generally was in short supply. Damien Hirst's old pal Sarah Lucas in the British pavilion was perhaps intentionally providing some light relief from the heavier concerns of the Biennale with a series of gigantic, spindly phalluses and plaster casts of her friends' naked bodies, with cigarettes up their orifices.

Only some of the British critics seemed to get this kind of smutty, lavatorial humor in the name of harsh realism.

Laughter and critical praise came together in the ostensibly more serious collaboration between India and Pakistan.

Neither country has a national pavilion, so they came together in spite of their political differences with an exhibition called My East is Your West.

A highlight here was an interactive video by Rashid Rana, in which the audience enters a room in Venice to be confronted with a full wall video screen of a family from Lahore in an identical room, smiling and waving and responding to us, while the audience attempted to engage them in a dance routine. A relationship that works fine in virtual reality, but of course can never happen.

A honey pot for dealers?

For some reason, there has been more comment about the commercial aspect of the Biennale this year than usual.

Although not ostensibly a selling event, it has also become, inevitably, a honey pot for dealers to promote their artists to the collectors who attend.

In the run up this year I must have received over a hundred emails from galleries whose artists are showing there.

The bigger international galleries like Hauser & Wirth or Continua have as many as thirteen artists exhibiting either in the official Biennale, or a collateral event. Artists showing outside the invited Biennale events are likely to be sponsored by interested backers. Ahmet Gunstekian from Turkey, for instance, had an exhibition sponsored by the Marlborough gallery in New York, who in turn were said to be have been sponsored by wealthy collectors who wanted to raise Gunstekian's profile.

The investment is significant. Even a small location outside the official event can cost 100,000 dollars to rent.

With the price of contemporary art escalating, that kind of outlay can be easily recouped. Most work you see at the Biennale is unobtrusively for sale.

Usually, the Biennale is held in June and collectors come from America and move on to Basel in Switzerland for the big contemporary art fair, where everything is openly for sale. 'See in Venice; buy in Basel', the saying used to go. But this year, Venice got together with Milan which hosts Expo 2015 through the end of October, and decided to bring its dates forward to present a united front.

Collectors will now go from Venice to Frieze New York which opens this week.

But for an idealist like Enwezor, this proximity to the market should not present a problem: Marx supported of the market, writing that no work of art was complete until it had been sold.

(CNN)