The Germany international will join Chelsea on July 1 from RB Leipzig after the clubs agreed a £47.5m deal.
"The discussions with the board at Chelsea were so good that I ultimately chose them," he told Sky Sports.
"In the conversations with me, the coach often emphasised how much he wanted me, how much he valued me as a person,.
"Of course it's hard to give up an oasis of wellbeing like the one I've had in Leipzig for years, but you can only get ahead in a career if you take the next step.
"This season was the crossroads, otherwise I would always have stayed with Leipzig. I've decided on something new and I hope that my form will continue like this."