If you've got legalistic Pharisaism, you haven't got the faith of God!
He found religious people tithing, giving a tenth, in a precise legalistic way, yet being fundamentally disobedient to God's word.
The genuine "sons of Abraham" are not legalistic Jewish Christians but those who simply possess faith in Jesus Christ.
It is plain, however, that on this external legalistic view of duty it was impossible to maintain a difference in kind between Christian and pagan morality; the philosopher's conformity to the rules of chastity and beneficence, so far as it went, was indistinguishable from the saint's.