Israel as a whole, excluding the believing remnant, failed to gain a righteous standing before God because she tried to win it with works. A stone on the racetrack over which she stumbled impeded her progress. Intent on winning in her own effort Israel failed to recognize the Stone prophesied in Scripture who was to provide salvation for her. [source][source][source]
The quotation is from Isaiah 8:14; Isaiah 28:16 (cf. 1 Peter 2:6-8). God intended the Messiah to be the provider of salvation. However the Jews did not allow Him to fulfill this function for them. Consequently this Stone became a stumbling block for them (cf. 1 Corinthians 1:23). [source][source][source]
Israel"s rejection of Jesus Christ did not make God unfaithful or unrighteous in His dealings with the nation. What it did do was make it possible for Gentiles to surpass the Jews as the main recipients of salvation. [source][source][source]