Both figures are richly dressed, adorned with the latest fashions of the time, which is very much a symbol of wealth and status. While it is a marriage portrait, love has little enough to do with marriage in the Northern Europe of the fifteenth century.

The work depicts a newlywed couple, and it is meant to honor their marriage through artistic depiction.

During the Renaissance, with a renewed focus on classical art and scientific understanding, visual arts underwent a significant change. In particular, religious themes dwindled in importance in comparison to classical subjects, and deeper, more varied colors were used to represent more realistic depictions of the human form.

Sandro Botticelli's The Birth of Venus is one of the signature paintings of Early Renaissance art from Italy, and as such deals with many themes prominent in the era. Botticelli chose the ancient goddess of love, appearing nude and fully formed from the ocean on a clam shell, instead of a Christian theme. Additionally, the picture's symbolism and color focus more on Platonic ideals than the Christian symbolism that was so prevalent in late Medieval art.

While Plato's Republic is a work of literature from Classical Antiquity, it is not so largely influential on the overall movement of Renaissance Humanism in literature and in art to be accurately described as the philosophical system at Humanism's core. Humanism was too broad a  movement to have its fundamental basis attributed to any one work.

The invention of the printing press gave way to an explosion in the manufacturing of books, many of which required illustrations to accompany the written word. This allowed for great expansion in the arts of printmaking and greatly increased the popularity of the medium, with its methods such relief (woodblock) printing, intaglio, etc. 

Mannerism lasted in Italy from the 1520s until the 1580s, but was practiced for a much longer amount of time in European countries north of Italy. Mannerist paintings portray subjects with purposefully elongated proportions and stylized poses. It was a step away from the harmonious, symmetrical, and rational subjects of Renaissance art.

It is speculated that in the aftermath of the Bubonic Plague, the citizens of Europe, and especially Italy, which was particularly devastated by the Plageu, began to think of life, spirituality, art, science, and the afterlife in a new way. This particularly traumatic event caused a social and economic upheaval in many parts of Europe, which changed the way of life and opportunities of many citizens.

These social, economic, religious and scientific changes in European culture may have sparked what is now known as the Renaissance.

The Annunciation Triptych, also known as the Mérode Altarpiece, is typical of a late medieval, early renaissance religious work of art that was designed to fit across the altar in a church. Usually paid for and commissioned by the civic leaders, such a work of art both held religious significance and demonstrated the wealth and prestige of the city. Robert Campin, and his Workshop, would have created the piece both as a matter of artistic skill and to show religious meaning.

Image is in the public domain, accessed through Wikipedia Media Commons: https://commons.wikimedia.org/wiki/File:Robert_Campin_-_Triptych_with_the_Annunciation,_known_as_the_%22Merode_Altarpiece%22_-_Google_Art_Project.jpg

Two significant, but very separate, movements pushed European painting forward in the fifteenth century. One was the Italian Renaissance, which focused on new methods of perspective and light. By contrast, Early Netherlandish Painting, centered in Flanders and represented by the Annunciation Triptych, used traditional methods of representation and posing, but made technical innovations in color and drawing that created more sharply defined and exquisite paintings. While the two would begin to learn from each other by the sixteenth century, Northern and Southern Europe continued to have separate traditions and styles in painting.

Image is in the public domain, accessed through Wikipedia Media Commons: https://commons.wikimedia.org/wiki/File:Robert_Campin_-_Triptych_with_the_Annunciation,_known_as_the_%22Merode_Altarpiece%22_-_Google_Art_Project.jpg