If we consider the sermon in its entirety:
أیها الناس شقوا أمواج الفتن بسفن النجاه و عرجوا عن طریق المنافره و ضعوا تیجان المفاخره أفلح من نهض بجناح أو استسلم فأراح هذا ماء آجن و لقمه یغص بها آکلها و مجتنی الثمره لغیر وقت إیناعها کالزارع بغیر أرضه.
فإن أقل یقولوا حرص على الملک و إن أسکت یقولوا جزع من الموت هیهات بعد اللتیا و التی و الله لابن أبی طالب آنس بالموت من الطفل بثدی أمه بل اندمجت على مکنون علم لو بحت به لاضطربتم اضطراب الأرشیه فی الطوی البعیده
This is one of his sermons, delivered after the Prophet’s death (PBUH), when addressing ʿAbbās and Abū Sufyān. After the events at Saqīfa, they had asked him to accept their pledge of allegiance.
“O people, cleave through the waves of discord in the ships of salvation. Turn aside from the path of enmity and division, and cast off the crowns of boasting and pride. Prosperous is the one who rises with support—or, lacking the means, withdraws in peace and leaves others undisturbed. Rule in this manner is stagnant water and a morsel that catches in the throat.
Whoever fails to pluck fruit when it is ripe is like a farmer sowing seed in someone else’s field.
If I speak of my worth and standing, they accuse me of coveting rule; if I remain silent, they say I fear death. Never! Not after all those struggles and battles! By God, the son of Abū Ṭālib is more familiar with death than an infant with its mother’s breast. Yet I am bound up with knowledge held in confidence: were I to disclose it, you would tremble like ropes lowered into a deep well.”
Nahj al-Balāgha, translated by Anṣāriyān, p. 64
The following points may be inferred:
When the companions of Saqīfa pledged allegiance and broke their covenant, leaving the Imam without support, he chose silence for the sake of the religion and did not rise to reclaim his right. He explains the reasons for his silence as follows:
He had no supporters.
If he rose under those circumstances, his companions would be put through hardship without achieving any result.
The interests of the religion required it.
The people of that time were not sufficiently prepared to understand or be governed by him.
The time was not right for an uprising. Under those conditions, rising would have the opposite effect: it would harm Islam without bringing any benefit to the religion.
He knew things of which you were unaware; were he to disclose them, you would be stunned and shaken.
As for the passage:
«بل اندمجت على مکنون علم لو بحت به لاضطربتم اضطراب الأرشیه فی الطوی البعیده»
The Imam is saying: I am bound up with hidden knowledge which, were I to reveal it, would make you tremble like ropes hanging down into a deep well.
The Imam possessed special, concealed knowledge. He knew things of which others were unaware. He was the Gate of the Prophet’s knowledge. In one respect, he held a divinely bestowed station of knowledge, just as he held the station of servanthood to God. He possessed the station of the Manifest Imam, in whom all things are recorded. He was, as it were, a divine supercomputer. He bore secrets entrusted to him by the Messenger of God: a thousand gates of knowledge, each of which opened onto a thousand more. He was more deeply versed in the secrets of the unseen realm, the heavens and their pathways. He knew the inner reality of matters, events and truths. He was the interpreter and clarifier of the Qur’an, which makes all things clear, and more besides.
The deep well may be a metaphor for hidden, inward knowledge—knowledge not everyone is capable of attaining. Anyone who yearns to reach it may, before getting there, find their thoughts and beliefs thrown into turmoil, losing both their faith and their worldly well-being. In other words, they lack the readiness and capacity to comprehend it.
This image, in its utter simplicity, is an outstanding expression of the intellectual and spiritual capacity of the people of that age.
أن رسول الله ص أسر إلی فی مرضه مفتاح ألف باب من العلم یفتح کل باب ألف باب و لو أن الأمه منذ قبض الله نبیه اتبعونی و أطاعونی لأکلوا من فوقهم و من تحت أرجلهم
سلونی [عما شئتم] قبل أن تفقدونی فو الله إنی بطرق السماء أعلم منی بطرق الأرض أنا یعسوب المؤمنین
لو أن الریاض أقلام و البحر مداد و الجن حساب و الإنس کتاب ما أحصوا فضائل علی بن أبی طالب ع