That is what we discovered on Wikipedia concerning the Songs Within the Key of Motown:

Songs in the Key of Life is the eighteenth studio album by the American singer, songwriter and musician Stevie Wonder. A double album, it was released on September 28, 1976, by Tamla Records, a division of Motown. The album is regarded as the culmination of Wonder's "classic period" of recording which began in 1972 with Music of My Mind.

By 1974, Wonder was one of the most successful figures in popular music; his previous albums Music of My Mind (1972), Talking Book (1972), Innervisions (1973), and Fulfillingness' First Finale (1974) were back-to-back critical successes. However, by March 1975, Wonder seriously considered quitting the music industry and emigrating to Ghana to aid children with disabilities. When plans for a farewell concert had already begun, Wonder changed his mind and signed a new contract with Motown on August 5, 1975. This outlined a seven-year, seven-album deal, with full artistic control. This deal included $13 million upfront, a potential bonus of up to $20 million, 20% of the royalties, and ownership of the publishing rights. At the time, it was the biggest recording deal in history.

Songs in the Key of Life was released as a double LP with a four-song bonus EP. It debuted at number one on the Billboard 200 chart, becoming only the third album to achieve that feat, and the first by an American artist. Both the lead single "I Wish" and follow-up single "Sir Duke" reached number one on the Billboard Hot 100. The album spent thirteen consecutive weeks at number one on the Billboard 200, becoming the album with the most weeks at number one during the year, and was the second-best-selling album of 1977 in the US. In 2005, the album was certified Diamond by the Recording Industry Association of America (RIAA), indicating sales of 5 million units for a double album.

The album won Album of the Year at the 19th Grammy Awards and is the best-selling and most critically acclaimed album of Wonder's career. It is now widely regarded as one of the greatest albums in the history of popular music, and many musicians have remarked on its influence on their own work. It was voted number 89 in Colin Larkin's All Time Top 1000 Albums and ranked number 4 on Rolling Stone's 2020 list of the "500 Greatest Albums of All Time". In 2002, the album was inducted into the Grammy Hall of Fame, and in 2005 it was inducted into the National Recording Registry by the Library of Congress, which deemed it "culturally, historically, or aesthetically significant".