This will depend on your job, of course.  Most times it will not matter to a lender, but for some, the effects of changing jobs can be disastrous to your application.

If you are working part-time, or a great deal of your income is from bonuses or overtime, you should talk to your lender prior to changing jobs.

If you are commissioned or self-employed, the lender likes to look at your past two-year track record.  Your lender can guide your decisions if you are thinking about buying a home.