Any such 'summary' would, inevitably, be opinion based.
Any supposed 'summary' of the word of Christ will diminish the whole volume of the words of Jesus and his ministry on earth during the days of his flesh (contained in four, separate accounts) and will diminish the doctrine of the gospel (expressed by six authors).
This diminishing will, invariably, err by its very paucity of expression and the error will be different, depending on who attempts the diminution.
Thus it results in an opinionated summary , as opposed to a body of authentic documentation.
The LAW may be summed up, and is, by Jesus of Nazareth, himself :
Therefore all things whatsoever ye would that men should do to you, do ye even so to them: for this is the law and the prophets. [Matthew 7:12 KJV.]
The Gospel of Jesus Christ and the Person of Jesus Christ : not so.
Many do, indeed, attempt a 'summary' and many (in my experience) express that 'summary' often from pulpit or platform, but starting from a different text each time and padding out the 'summary' appropriately.
But it is always the same (in these instances that I have witnessed) : a diminution of the breadth of the gospel into a much reduced - and 'personalised', opinionated - form.
The epistles and the gospel accounts are the form and the content that they are for there is much to be conveyed of the Person, the Work, the Offices and the Ministrations of Jesus Christ and the Spirit of Christ, and the overseeing of God and the Father.
Like any body of truth, this cannot be diminished - or 'dumbed down'. It must be expressed in its entirety or large parts of the Gospel of Jesus Christ will, generation by generation, be eroded and be let slip, through neglect and through unavoidable ignorance.
One may sum up the focus and the intent of Jesus' teaching - and John the apostle does so :
And this is his commandment, That we should believe on the name of his Son Jesus Christ, and love one another, as he gave us commandment. 1 John 3:23.
But in order to fully appreciate these momentous words, one needs all the others - initially - that one might understand the depth, the profundity and the implications of this succinct crystallisation.