What is the relationship between patience and kindness? I was just reading some of the commentarial literature in the Pali Canon and it occurred to me that there seems to be some kind of relationship between patience and kindness that I don't fully understand but would like to get clarity on.
Kindness is descriptive of a wholesome state of mind encompassing love and compassion. These states of mind arise in the absence of states of mind having greed, anger and delusion. 

Patience is the characteristic of bearing with some form of suffering (physical and/or mental). Being able to bear with suffering prevents mind states based on anger from arising. Hence developing patience allows one to bear with suffering without allowing anger to arise, which allows kindness to blossom.

This is the relationship between patience and kindness. 

Although this is not your question, how is one able to bear with suffering and therefore develop patience? By seeing reality clearly. How does one see reality clearly? By paying attention to the four foundations of mindfulness.

So, practising the four foundations of mindfulness allows one to be patient such that anger does not arise while experiencing suffering, thus allowing one to be kind.