Are Sundays the Real Day to Serve God.

I write this with a lot of questions in my head, I have observed even while growing up that most people are more in tune with their spiritual self on Sundays than any other day in the week, they (if married abstain from sex) they try to be bold and also be free from sin.
A lady said she smokes but she doesn't smoke on Saturday close to Sunday, and she abstains from sex as much as she can but on Monday she doesn't abstain because she likes it.
When Christ was talking to the Samaritan woman at the well, he said a time will come when people will not need to go to the mountains or hills to pray or worship. What did he mean?