In The Name of Allaah, The Most Merciful, The Bestower of Mercy

”He (Yusuf) knew that he is not able to avert it on his own, and that if his Lord did not protect him and avert their (i.e. the women) plot, he would have inclined towards them by way of (human) nature and thus become of the ignorant ones.  This is from Yusuf’s perfect knowledge about his Lord and himself (as a human being). [Updated: Sharh Al-Asbaab Wal-Amaal Alatee Yudaa-afu Bihaa Ath-Thawaab of Imaam as-Saa’di page: 58:see link: http://www.salafitalk.net/st/viewmessages.cfm?Forum=29&Topic=9966: Post Number 6]

Additional Detail for more clarity

Concerning the Aayaat 23 and 24 Soorah Yusuf:

‘’And she, in whose house he was, sought to seduce him (to do an evil act), she closed the doors and said: “Come on, O you.” He said: “I seek refuge in Allah (or Allah forbid)! Truly, he (your husband) is my master! He made my stay agreeable! (So I will never betray him). Verily, the Zalimun (wrong and evil-doers) will never be successful.” [Ayah: 23]

‘’And indeed she did desire him and he would have inclined to her desire, had he not seen the evidence of his Lord. Thus it was, that We might turn away from him evil and illegal sexual intercourse. Surely, he was one of Our chosen, guided slaves.’’[Ayah:24]

Imaam as-Saa’di (rahimahullaah) said about the part of the verse: ‘’Had he not seen the evidence of his Lord;’’ That is what he possessed of knowledge and Eemaan which necessitates abandonment of everything that Allaah has forbidden—and which necessitated that he would distance himself and abstain from this major sin, and he (Yusuf) said: “I seek refuge in Allah (or Allah forbid)! That is: I seek refuge with Allaah that I should (ever) commit this ugly deed, because it is from that which angers Allaah….

Concerning the Ayah:

‘’Unless You turn away their plot from me, I will feel inclined towards them and be one (of those who commit sin and deserve blame or those who do deeds) of the ignorants.’’ [Noble Qur’aan- Shaikh Taqiyudeen Al-Hilaali and Dr Muhsin khan. Soorah Yoosuf Ayah: 33]

Imaam Ibn Katheer (rahimahullaah) said:

‘’If You abandon me and I am reliant on myself, then I have no power over myself, nor can I bring harm or benefit to myself, except with Your power and will. Verily, You are sought for each and everything, and our total reliance is on You Alone for each and everything. Please, do not abandon me and leave me to rely on myself.’’ [Tafseer Ibn katheer]

Conclusion:

So, Yusuf (alayhis-salaam) relied upon Allaah and acknowledged the absolute Power and Might of his Lord in repelling harm and bringing benefit, and that he cannot repel harm or bring benefit except by the Might and Power of his Lord.  And his knowledge and awareness of Allaah, and Imaan in Allaah necessitated that he greatly abhorred the evil deed he was been called to, and he was definitely going to turn away from it by the will of Allaah (The Most High).  Thus Imaam as-Saa’di said: ‘’That is what he (Yusuf) possessed of knowledge and Eemaan which necessitates abandonment of everything that Allaah has forbidden—and which necessitated that he would distance himself and abstain from this major sin…’’