Praise be to Allah, and peace and blessings be upon the Messenger of Allah. To proceed:
The Sirat is established by the Qur’an, the Sunnah, and scholarly consensus. It is a bridge stretched over the back of Hell, which people cross on the Day of Resurrection. The believers cross it according to their deeds: some of them pass like lightning, some like the wind, while some are scratched by hooks or seized by them and fall into the Fire.
Allah Almighty says:
﴿There is none of you except that he will come to it. This is upon your Lord a decree that must be fulfilled Then We will save those who were mindful of Allah, and We will leave the wrongdoers therein on their knees﴾ [Maryam: 71-72].
It is authentically reported in the two Sahihs from Abu Sa'id Al-Khudri, may Allah be pleased with him, in the hadith describing the bridge, that people cross it according to their deeds. Some are saved, some are scratched, and some are thrown headlong into the Fire of Hell.
The Sirat comes after the reckoning. The reckoning takes place before people cross it. After they know what their outcome will be, the Sirat is placed over Hell. The believers then cross it, and a believer does not have complete assurance of being saved from the Fire until he has crossed the Sirat.
This does not mean that the reckoning has no purpose. The reckoning makes clear people’s deeds, their recompense, and what they deserve. Then crossing the Sirat is another stage of the Hereafter, in which the differences between people according to their deeds become manifest. Some are saved, while others fall.
There is no contradiction between the two, because Hell has gates, levels, and depths. The falling of some sinners from the Sirat into the Fire does not mean that they do not enter it through its gates. Rather, they fall into its various levels according to what Allah has decreed for them.
Allah Almighty says:
﴿It has seven gates; for each gate is a portion of them assigned﴾ [Al-Hijr: 44].
The verses that speak of the disbelievers being driven to the gates of Hell concern their entering it. The disbelievers do not cross the Sirat at all. Rather, they are brought to the Fire before the Sirat is set up, as indicated by authentic hadiths.
As for the Sirat, it is crossed by the people of Tawhid, including sinful believers who affirm the Oneness of Allah. Whoever passes safely enters Paradise, while whoever among the sinful believers falls from it enters the Fire according to the extent of his sins. Then Allah may bring him out of it by His mercy.
The Sirat is a firmly established reality. It is not merely a metaphorical path or simply a reference to deeds; rather, it is a real bridge over Hell, and crossing it takes place after the reckoning.
There is no contradiction between the Sirat and the reckoning, nor between some people falling into the Fire and Hell having gates. The disbelievers enter the Fire before the Sirat, whereas the people of Tawhid cross it. Some are saved and some fall.
It is obligatory, regarding matters of the unseen, to accept what has been authentically established from Allah and His Messenger, peace and blessings be upon him, and not reject authentic texts because of doubts or abstract reasoning alone. If something in these texts appears difficult to understand, one must refer back to qualified scholars.
And Allah Almighty knows best.