Kehrer joined West Ham in August from Paris St Germain where he made 34 appearances in all competitions last season.
"I wanted to have the best rhythm and be fully fit and competitive for the World Cup. That was a major reason for me," Kehrer told a news conference from Germany's Al Shamal training base in northern Qatar on Sunday.
"It has paid off so far. I have played all the matches in the Premier League for West Ham. It was a big challenge and that's what I was looking for and it is a very good preparation for the World Cup."
A fit Kehrer is key for the German defence and the versatile full back has played more than any other international team mate since coach Hansi Flick took over from Joachim Loew last year.
"I feel the confidence of Hansi and you can see that in those facts (playing time). I give it all to pay back this trust," he said.
It is still not clear, though, where Kehrer be deployed with Germany preparing for their first World Cup Group E match against Japan on Wednesday. He has also been deployed as a defensive midfielder.
"I have played central defender but also as full back on both sides and I feel well in any of the positions. I have no problem to change."
Germany also face Spain and Costa Rica in their group.
