Adam Clarke on Luke 7:29

Justified God - Or, declared God to be just - εδικαιωσαν τον Θεον. The sense is this: John preached that the Divine wrath was coming upon the Jews, from which they might flee by repentance, Luk 3:7. The Jews, therefore, who were baptized by him, with the baptism of repentance, did thereby acknowledge that it is but justice in God to punish them for their wickedness unless they repented, and were baptized in token of it. Bp. Pearce proves that this is the sense in which the word δικαιοω is used here and in Psa 51:4, compared with Job 32:2, and by this evangelist again in Luk 10:29, and Luk 16:15.