The former Juventus goalkeeper has come out of retirement to join after Marc-Andre ter Stegen's season was ended by a knee injury.
Laporta said: "We needed three top-quality goalkeepers after Ter Stegen's injury. Iñaki and Ander are young and we needed one with more experience.
"He's a proven goalkeeper, with experience, he imposes himself. We have the same goalkeeping position now as when Ter Stegen was there, but with his injury we had been reduced to two goalkeepers and we needed another one."
Laporta also revealed the terms of Lewandowski's renewal this season.
He told Barca One: "Barça is a fair club, it always has been. We have renewed Araujo, De Jong and Pedri. Gavi will have it soon. Lewandowski will renew if he plays 50% of the games (his contract expires) and Raphinha's contract expires in 2027.
"We will be fair to everyone. Lamine? He has a contract and it is Deco who makes the decisions, but he has instructions from the board in this regard."