The LORD is well pleased for his righteousness' sake; he will magnify the law, and make it honourable.
The Lord is well pleased for his righteousness' sake - not His people's, but His own; Isaiah 42:24 shows that they had no righteousness (Isaiah 45:24; Isaiah 59:16; Isaiah 64:6.) God is well pleased with His Son ("in whom my soul delighteth," Isaiah 42:1) who "fulfills all righteousness" (Matthew 3:15) for them, and is well pleased with them for His sake (cf. Isaiah 42:6; Psalms 71:16; Psalms 71:19; Matthew 5:17; Romans 10:3-4; Philippians 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.