This is because they might be able to deceive the believers, but will never be able to deceive Allah U, as Allah U Knows all the secrets and that which is yet more hidden, as He says,

﴾وَإِنْ تَجْهَرْ بِالْقَوْلِ فَإِنَّهُ يَعْلَمُ السِّرَّ وَأَخْفَى﴿

“And if you speak aloud – then indeed, He knows the secret and what is [even] more hidden.” [Surah Taha: 7].

Secrets are normally between two people. What then, is more hidden than a secret? It is what you conceal in yourself that no other person knows of. Hence, you will never be able to deceive Allah U, as the Holy Qur’an says:

﴾وَمَا يَخْدَعُونَ إِلاَّ أَنفُسَهُمْ وَمَا يَشْعُرُونَ﴿

“but they deceive not except themselves and perceive [it] not.”.

 And in another verse:

﴾لا يَعْلَمُونَ﴿

“they know [it] not.” [Surah Al-Baqarah: 13].

The difference between these two verses is that when the topic discussed is faith, Allah U says: ﴾لا يَعْلَمُونَ﴿ “they know [it] not.” but when hypocrisy is discussed, Allah U says: ﴾وَمَا يَشْعُرُونَ﴿  “and perceive [it] not”. This is because, faith is an unseen matter which needs knowledge, whereas hypocrisy and deception are things which are tangible and can be perceived, so the phrase: ﴿وَمَا يَشْعُرُونَ﴾  “and perceive [it] not” is most suited to them.