I have always respected Nicolas Poussin's paintings, but often without really getting excited about them. They come across as resolutely independent, wonderfully composed and prepared, but often a little too intellectual for my taste.

Then there is always the moment when one sees something that stops one in one's tracks and aha!, you begin to understand and appreciate in a different way. That happened to me with some of Poussin's paintings in the beautiful Dulwich Picture Gallery this week.

An aside: the elegant small gem of Dulwich Picture Gallery, part of Dulwich College, (a large and independent school founded in 1619 in Greater London), is housed in a gallery designed by Regency architect, Sir John Soane. The Gallery, the first British art museum, was opened to the public in 1817.

Among their many Old Master paintings is a collection of Poussin paintings. Added to that number at present is a loan from the Duke of Rutland, three of Poussin's Seven Sacraments, a first series of paintings he did as a commission in 1637-1642 for his friend and patron, Cassiano dal Pozzo, secretary to Pope Urban VIII's nephew. Poussin had moved to Rome at the age of 30 and was in a small circle of erudite intellectuals around the Pope; Nonetheless he did not seek to make his way by competing to paint large Baroque works for churches and other public spaces, as did all his contemporaries. He quietly went his own way, following the idea that painting could convey ideas and emotions more eloquently than words. His images were intense, erudite and passionate in his beliefs.

In this series of the Seven Sacraments, Poussin set out to paint not only arresting, powerful evocations of Baptism, Confirmation, Marriage, Ordination, Penance, the Eucharist and Extreme Unction, the sacred rites of the Roman Catholic Church. He also wrestled with central questions of what each sacrament meant in terms of faith and practice, thus imparting a feeling of experimentation and deep intimacy. By united historical (often architectural) details with telling gesture, and contemporary details, he managed to unite emotional power with current relevance, so important to his viewers. As you look as these paintings, they convey a powerful message of ritual down the ages, and remind us of the how important to each of us it is to share experiences, both personal and communal. Interestingly enough, the concept of the Sacraments in art was more a subject favoured by Northern artists, such as Rogier van der Weyden; Italian artists preferred other approaches to sacred art.

Poussin the artist was a perfectionist. He himself said, "I neglected nothing". When preparing for a painting, he would set up a small box like a miniature theatre; he then used small wax models that he moved around until he had achieved the perfect composition and accurate depictions of light and shade, carefully considering every juxtaposition, every rhythm, every placement of figures cascading into the drama of each scene.

As was remarked in the statement about the Poussins in the Dulwich Picture Gallery, "The Sacraments are the sum of what art can do, not only in terms of line, colour and light, but also with regard to the intellectual, emotional and spiritual experience of the viewer."

These Seven Sacrament paintings were acquired by the 4th Duke of Rutland in 1786. (Poussin had finished this series in 1642 and later painted a second Sacraments series for the French Ambassador to Rome.) Sir Joshua Reynolds, the first President of the Royal Academy, championed their arrival in England and helped perhaps even with the very elegant, classical-style framing. One painting, Penance, was destroyed by fire at Belvoir Castle in 1816; three have been sold over the years. Baptism is in the National Gallery in Washington, Ordination is at the Kimball Art Museum and Extreme Unction is now at the Fitzwilliam Museum in Cambridge. The three remaining in the Duke's possession, Confirmation, Marriage and Eucharist, are the ones I saw at Dulwich.

They are indeed amazing. Very theatrical and on a shallow plane - understandable given Poussin's working methods of composition - they are an elegant symphony of line, colour and placement to convey the deep faith and importance of each sacrament, its holy moment and its celebration. Solidity and links with the past are conveyed by classical columns that frame and highlight the luminous, subtle colouring that dances across the canvases.

As I studied these three wonderful paintings, I understood more why Poussin has influenced so many important artists that came after him. Classical artists like David or Ingres learned from him; Cezanne and Picasso did so too. Poussin even heralded Mondrian and Rothko with his vigorous compositional sense and understanding of the power of colour. I came away from the Dulwich Picture Gallery feeling I had finally met Nicolas Poussin properly for the first time.