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.
163) maintains that "he was himself not a Pietist," as he did not advocate the quietistic, legalistic and semi-separatist practices of Pietism, though they were more or less involved in the positions he assumed or the practices which he encouraged or connived at.
He found religious people tithing, giving a tenth, in a precise legalistic way, yet being fundamentally disobedient to God's word.
If you've got legalistic Pharisaism, you haven't got the faith of God!