Picture Courtesy: https://balance.media/kindness/
The cold can be anywhere from annoying to life-threatening. Winter is considered as harsh, cold, bleak and gloomy. It is the kind words that can warm.
In reality, it does nothing to the temperature of those winter months, but it's a metaphor, so it doesn't have to. Some words warm your heart a little. Therefore, one should always talk politely with everyone and never use harsh words with anyone.
'A kind word can warm three months of winter' means they will be happy and contented, and even you will feel good because you have done something good for them.
Pestalozzi Children's Village, India.