1) Central figures in medieval art were mostly religious motifs or emperors which were presented as if they were saints. Commonly, paintings or frescoes in buildings would show great kings building monasteries or helping people or similar things.
2) Religious motifs were mostly depicted in art at the time. Pictures were often of Jesus Christ and his sacrifices or of him helping people or other saints. In that period, art had to be bigger than people and had to serve a function for people and present religious beliefs.
3) Nowadays art is more complex. At that time art didn't presume that self-reflection would be involved while understanding art nowadays has a huge degree of analysis and self-reflection on what has been seen. Also, nowadays art isn't about religion or kings but rather about abstract concepts.