The purpose of Laim's blog is: to advertise his window washing service
We can drive to conclusion by reviewing the sentences that Liam use.
This line:
. . . If it’s spring cleaning time at your house, please consider giving me a call . . .
Provide the readers with the information that Liam is currently open to receive any request for cleaning houses.
And this line:
. . . We supply all of our own equipment and leave your house sparkling clean. Our service is guaranteed! . . .
Is made to show the competitive advantage that Liam's service has over other options.