"I am very pleased to have been called up," said Bairstow, who is set to bat at number five for England after being included in a 13-man test squad.
"Consistency-wise I think I am in my best form and striking the ball well and hopefully this will continue.
"Playing international cricket is a great challenge but that is why we play the game.
"If you don't challenge yourself you will never find anything out about yourself."
Bairstow's previous stints in international cricket have seen questions raised over his ability to play short-pitched bowling - something he is sure to face from the likes of Australia's Mitchell Johnson, Mitchell Starc and Josh Hazlewood.
But Yorkshire coach Jason Gillespie, a former Australia fast bowler, said Bairstow was now a much-improved batsman.
"It is important that those people who don't watch much county cricket don't pipe up with opinions based on his past experience in test cricket because we're talking about a different beast right now," Gillespie wrote in his Guardian column.
Ballance has an impressive average of nearly 48 in his 15-test career but the left-hander has struggled this season, with only 134 runs in eight test innings against New Zealand and Australia this season.
The 25-year-old scored three hundreds and two 50s in his first 10 innings for England but has found scores harder to come by of late.
"He has scored a heck of a lot of runs over a short period of time," Bairstow, also 25, said of Ballance.
"But it is just one of those disappointing things and, hopefully, I will be able to get in and score runs.
"I have been very positive at the crease this season and will try and take that into the Ashes series."
England third test squad
Alastair Cook (c), Adam Lyth, Ian Bell, Joe Root, Jonny Bairstow, Ben Stokes, Jos Buttler, Moeen Ali, Stuart Broad, Mark Wood, James Anderson, Adil Rashid, Steven Finn.
- AAP
