don't admit anyone into the Community, unless he has professed the truth of the Pure Imáms,

Shoghi Effendi emphasized that the Bahá'ís believed in the station of the Imáms: 

The Bahá'ís are the only people who can prove the right of the Pure Imáms. Bahá'u'lláh proved their right in 'The Book of Certitude'. The friends of the West will prove their right and will promulgate Islam. This is an essential belief in our Faith. We acknowledge the validity of the Imámate Institute and the invalidity of the Caliphate. The greatest proof is the collapse of the Caliphate after thirteen centuries.

[...]

For the sake of this point, teaching the Faith to the Shi'ah is easier than to the Sunnîs... But, this is the belief of the people of Bahá... So don't admit anyone into the Community, unless he has professed the truth of the Pure Imáms,

(Shoghi Effendi Through the Pilgrim's Eye, Volume 1 by Earl Redman - GEORGE RONALD, OXFORD)