Sirat e mustaqeem means the straight path. Allah give us two things for the Sirat e mustaqeem the Holy book means Quran e majeed and walayat e Ali A.S.
to need both for the sirat e mustaqeem.
who take the Quran leave the walayate Ali a.s this is not complete who take the walayat e ali as Leave the Quran its also Un complete need for the sirat e mustaqeem both Quran and walayate Ali a.s.
(Al Ali un maal quran Alquran o maa Ali a.s)