Livermore was last called up as a late replacement for friendlies against Brazil and Germany and Southgate has said his 'loyalty to the cause' is what has helped him retain his place.
"We've played Jake in several matches and he's done a job for the team. In November, we left him out, and he was just about to board a plane.
"He left the family at the airport, he came in, he did really well for us against Germany and Brazil, and I think that has to carry some weight when you are building the spirit and culture around your team.
"That doesn't mean he is guaranteed to go in the summer, but I think it justifies him staying in our squad, because he has been an important member of our squad in building what we want to build in terms of togetherness and spirit.
"That is the sort of example of sacrificing what you are doing for the team that I think is important.
"So I get that, I know when I pick Jake it is going to get a certain sort of reaction. But there is a specific reason for why we have done it this time in particular."
Livermore was picked ahead of midfielders such as in-form Jonjo Shelvey and Chelsea duo Ross Barkley and Danny Drinkwater.