Harper will make his Major League debut on Saturday, and he will hit seventh in the lineup. He will also become the everyday left fielder, meaning that the platoon between Xavier Nady and Roger Bernadina is over.
"We can use the left-handed bat in Harper," manager Davey Johnson said. "I'm going to put him in left field and let him play. So he was a natural pick. He has been swinging the bat well."
Harper is on the 25-man roster because third baseman Ryan Zimmerman was placed on the disabled list with inflammation in his right shoulder.
Zimmerman believes that promoting Harper is a wise move.
"Bryce is a very talented player. He can help us win," Zimmerman said. "He is someone we want on our team. He can help us in a lot of ways."
Zimmerman considers Harper mentally tough and able to handle the Major Leagues. It helps, Zimmerman adds, that Harper spent the last two Spring Trainings with the big club. In fact, Zimmerman sees a much more mature Harper than he did in 2011.
"I think him being in Spring Training the last couple of years and getting to know us all -- and us getting to develop relationships with him -- makes it easy for him to come up and ask questions. It makes it easy for us to help him. That will help out a lot.
"Not so much anymore, but Bryce had a different way of expressing his confidence. From Spring Training [in 2011] to this Spring Training, I've never seen anyone grow up as much as he has -- with the way he carries himself, the way he thinks things differently now. Not to say that two years ago he was a bad person. He is a great kid. He means well. He works hard. He plays the game the right way. You never have to worry about him playing hard. Like I said, when you are 19, you do stupid stuff. Bryce's stuff was on SportsCenter. ... He has learned a lot."
Zimmerman didn't elaborate on the "stupid stuff," but video of Harper blowing a kiss at a Minor League pitcher he'd tagged for a homer went viral and sparked a fair amount of criticism.
If he were to give Harper advice, Zimmerman would say, "Baseball is baseball. Obviously, this is the highest level of baseball compared to anything. But the bases are the same, the pitching mound is the same. ... You realize it's the same game he has played his whole life."
Outfielder Jayson Werth believes Harper will learn a lot in the big leagues.
"He will pick up stuff quick. I think he can help us," Werth said. "We're banged up. I think he fills a hole for us. ... It's an exciting time for baseball, for this team and for Bryce, himself, and we'll see what happens."
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.