Jamieson, Fausset & Brown

his righteousness--not His people's, but His own; Isa 42:24 shows that they had no righteousness (Isa 45:24; Isa 59:16). God is well pleased with His Son ("in whom My soul delighteth," Isa 42:1), "who fulfils all righteousness" (Mat 3:15) for them, and with them for His sake (compare Isa 42:6; Psa 71:16, Psa 71:19; Mat 5:17; Rom 10:3-4; Phi 3:9). Perhaps in God's "righteousness" here is included His faithfulness to His promises given to Israel's forefathers [ROSENMULLER]; because of this He is well pleased with Israel, even though displeased with their sin, which He here reproves; but that promise could only be based on the righteousness of Messiah, the promised seed, which is God's righteousness.