Allah - the Most Perfect, the Most High - responded to the supplication of His Prophet Ibrahim - 'alayhis-salam - when he said:
"Our Lord! Send unto them a Messenger from themselves, reciting to them Your Signs, teaching them the Book and the Wisdom and purifying them. Indeed You are the Most Powerful, the Most Wise."[Al-Qur'an 2:129]
So Allah - the Mighty and Majestic - said:
"It is He who has sent to the unlettered ones a Messenger from amongst themselves, reciting to them His Signs, purifying them and teaching them the Book and the Wisdom, whereas before that, they had been in clear misguidance."[Al-Qur'an 62:2]
So the Prophet 'alayhis-sallatu was-salam has two tasks: ta'lim (teaching) and tazkiyah (purification). And Ibrahim - 'alayhis-salam - mentioned ta'lim before tazkiyah. And Allah - the Mighty and Majestic - answered him, but by giving tazkiyah precedence to ta'lim.
And Allah blessed the Believers by sending the Messenger, who carried out these two tasks, so He - the Mighty and Majestic said:
"As We sent to you a Messenger from amongst yourselves, reciting to you Our Signs, purifying you, and teaching you the Book and the Wisdom, that which you did not know."[Al-Qur'an 2:151]
So in this ayah also, Allah - the Mighty and Majestic - mentions tazkiyah before ta'lim. Thus, as is known, tazkiyah (purification) is one of the fruits of acting upon knowledge; and that knowledge causes harm for its possessor if it is not accompanied by action. Thus, whosoever increases in knowledge, but does not increase in taqwa (piety and obedience to Allah), then let him be suspicious about his knowledge.
And our Salaf (Pious Predecessors) used to inherit tazkiyah from each other, as part of good and fine manners. This was due to their sitting with the Shaykh and accompanying him. So 'Abdullah ibn Maslamah al-Qa'nabi (d. 221H) said: "We used to sit with Imam Malik and take from his manners and conduct, just as we would take from his knowledge."
However, in the later generations, Shari'ah knowledge has almost become restricted to just colleges and universities and sitting in front of the doctors and teachers for short periods of time. So the students do not take any benefit from good manners and conduct - even if those teachers have a share of it. And we often see and hear about many shortcomings of both the students and the teachers!
Thus, the Din has become weak, yaqin (certainty of faith) has dwindled, sabr (patient perseverance) - with its wide Islamic understanding - has passed away, as has zuhd (praiseworthy abstinence from the world) - except for those whom my Lord has mercy upon.
So knowledge alone, without good manners and conduct, will not produce any fruit in a way that the people can be benefited by its possessor - from what is seen and what is spoken. And through seeking knowledge alone, the Muslims will not be saved from hypocrisy. Rather, seeking knowledge must be accompanied by good manners and conduct, so that he remains safe, derives benefit and is saved from sin and its causes, and also from being burdened. This is attested to by what At-Tirmidhi authentically relates in his Sunan (no. 2837), from Abu Hurayrah - radhiallahu 'anhu that the Prophet sallallahu 'alayhi wa sallam said: "Two qualities do not come together in a hypocrite: Good manners and conduct, and the understanding of the Din."
So in this hadith, good manners and conduct are mentioned before understanding of the Din. Indeed, the greatest and most valuable fruits of tazkiyah (purification) are sabr (patience) and zuhd (abstinence from the non-beneficial things of this world) and the greatest and most precious fruits of 'ilm (knowledge) is yaqin. So he who gains them both in this way, then he is an Imam of the Din; and this is testified to by the saying of Allah - the Most High:
"And We made from them leaders, giving guidance by Our Command, whilst they had sabr (patient perseverance) and had yaqin (certainty) in Our Signs."[Al-Qur'an 32:24]
So sabr is the fruit of tazkiyah, whilst yaqin is the fruit of 'ilm. And here also, sabr is mentioned before yaqin. Shaykh ul-Islam Ibn Taymiyyah (d. 728H) used to say: "Through sabr and yaqin leadership in the Din is attained." [Quoted by Ibn Al-Qayyim in Madarijus-Salikin (2/154)] Yes, indeed! That is so because he who gains them both, then he has attained and actualised the two tasks of Allah's Messenger sallallahu 'alayhi wa sallam, and has thus become an inheritor of the Prophet and he is the leader of all the Imams.
Finally! We must draw attention to the fact that the Salaf us-Salihin (Pious Predecessors) - may Allah be pleased with them all - actualised these two tasks and therefore they achieved rectification of themselves and rectification of others. 'Abdullah ibn Al-Mubarak (d. 181H) used to say: "The latter part of this Ummah will not be rectified, except by that which rectified its first part: zuhd and yaqin." And zuhd cannot be attained except by means of sabr, which cannot be attained except through tazkiyah (purification). And yaqin cannot be attained except through purified Shari'ah knowledge. So would that we had realised that our misfortune lies in the absence of these two matters from our lives, and that he who calls to them - persisting in this and refusing to be pre-occupied from them by anything else - then he is upon the correct manhaj (methodology) and upon the Straight Path.