“To get the best interest rates, you’ll want to be pre-approved by a mortgage specialist who works with multiple lenders . They’ll be able to compare lenders and shop around for the loan terms that best fit your budget.” Not sure about why a pre-approval can make such a difference? Check out this article from the Financial Post:
https://financialpost.com/moneywise/what-is-a-mortgage-preapproval-and-how-long-does-it-last