So the story begins at the time of Moosa AS with Bani Israel gathered around him, as mentioned in Sahih al-Bukhari.
عَنِ أُبَىُّ بْنُ كَعْبٍ قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ ‏ “‏ بَيْنَمَا مُوسَى فِي مَلإٍ مِنْ بَنِي إِسْرَائِيلَ جَاءَهُ رَجُلٌ، فَقَالَ هَلْ تَعْلَمُ أَحَدًا أَعْلَمَ مِنْكَ قَالَ لاَ‏.‏ فَأَوْحَى اللَّهُ إِلَى مُوسَى بَلَى عَبْدُنَا خَضِرٌ‏.‏ فَسَأَلَ مُوسَى السَّبِيلَ إِلَيْهِ، فَجُعِلَ لَهُ الْحُوتُ آيَةً، وَقِيلَ لَهُ إِذَا فَقَدْتَ الْحُوتَ فَارْجِعْ، فَإِنَّكَ سَتَلْقَاهُ‏.‏

Hadhrat Ubai bin Ka`b (RA) narrates that he heard Allah’s Messenger (ﷺ) saying, ‘While Moosa was sitting in the company of some Israelites, a man came and asked (him), ‘Do you know anyone who is more learned than you?’ Moosa replied, ‘No.’ So, Allah sent the Divine Inspiration to Moosa: ‘Yes, Our slave, Khadir (is more learned than you).’ Moosa asked how to meet him (i.e. Khadir). So, the fish, was made, as a sign for him, and he was told that when the fish was lost, he should return and there he would meet him.

Musa عليه السلام referencing the most amount of knowledge to himself was on account of him being a Prophet amongst his people, and he understood the question to refer to the mortals or human beings, in other words Musa عليه السلام understood the question to mean, “From the Bani Israel, is there anyone who has more knowledge than you (on matters of Tauheed etc?)” Allah then revealed to Musa عليه السلام that despite him being a Prophet, there is a slave of His that is more knowledge than him.

So even before the journey had begun, we can extract the first benefit. A person should never be impressed with himself no matter how much knowledge he has. As students of knowledge, we should always remain humble. The reality is it is only when a person attains more knowledge, that he actually realises how little knowledge he had.

This is Allah’s habit with His elect lovers, that whenever they display any strength or transgress, by the smallest distance, the limits of slave-hood, He will discipline them with someone who is lower than them in knowledge and status, as a protection and ennoblement for them, so that they will not stop short of the highest perfection.

An individual has to refer knowledge back to Allah because all knowledge comes from Allah. No matter how much we try, we will never acquire knowledge except by the permission of Allah. The knowledge that we do have, should make us constantly ask Allah to bestow more knowledge on us. Take note of what Allah told the Prophet ﷺ:
وَقُل رَّبِّ زِدْنِى عِلْمًا
“Say: My Lord, increase me in knowledge.” [TaHa: 114]

There is no one who knows everything. Allah gives certain knowledge to whoever He wills. Musa عليه السلام didn’t link his knowledge to Allah. All the knowledge that we have is from Allah and we need to thank Him.

At the same time remember that half of wisdom is the ability to say لا ادري “I don’t know”. There is nobody in this world who knows everything and when we admit that we don’t know we are just acknowledging the truth.