From the Lambda documentation: https://docs.aws.amazon.com/lambda/latest/dg/welcome.html
“Lambda is a compute service that lets you run code without provisioning or managing servers. Lambda runs your code on a high-availability compute infrastructure and performs all of the administration of the compute resources, including server and operating system maintenance, capacity provisioning and automatic scaling, code monitoring and logging.” When you “deploy” your code, you are making it live. Until you “deploy” your code, it will not execute any action. For example, if the code is processing data uploaded to an S3 bucket, it will not actually start taking that action until the code is deployed. This is also true for any changes done to already existing functions.