Because the sons
ben (bane)
a son (as a builder of the family name), in the widest sense (of literal and figurative relationship, including grandson, subject, nation, quality or condition, etc.
of Jonadab
Yhownadab (yeh-ho-naw-dawb')
Jehovah-largessed; Jehonadab, the name of an Israelite and of an Arab -- Jehonadab, Jonadab.
the son
ben (bane)
a son (as a builder of the family name), in the widest sense (of literal and figurative relationship, including grandson, subject, nation, quality or condition, etc.
of Rechab
Rekab (ray-kawb')
rider; Rekab, the name of two Arabs and of two Israelites -- Rechab.
have performed
quwm (koom)
to rise (in various applications, literal, figurative, intensive and causative)
the commandment
mitsvah (mits-vaw')
a command, whether human or divine (collectively, the Law) -- (which was) commanded(-ment), law, ordinance, precept.
of their father
'ab (awb)
father, in a literal and immediate, or figurative and remote application) -- chief, (fore-)father(-less), patrimony, principal. Compare names in Abi-.
which he commanded
tsavah (tsaw-vaw')
(intensively) to constitute, enjoin -- appoint, (for-)bid, (give a) charge, (give a, give in, send with) command(-er, -ment), send a messenger, put, (set) in order.
them but this people
`am (am)
a people (as a congregated unit); specifically, a tribe (as those of Israel); hence (collectively) troops or attendants; figuratively, a flock -- folk, men, nation, people.
hath not hearkened
shama` (shaw-mah')
to hear intelligently (often with implication of attention, obedience, etc.; causatively, to tell, etc.)
unto me