Lilly I believe there were later agreements that reconciled the contradictions.
You are probably talking about the Churchill White Paper.
It tried to resolve the contradictions but it did not succeed. They could not promise land to some people in exchange for a specific action, and then give it to other people after that action was performed, and then put the whole affair to rights by composing an eloquent phrase or two.
Here is what happened, according to
http://www.mideastweb.org/1922wp.htm
Soon after the Balfour Declaration was issued, it became clear to the British that it was inconvenient to implement a "National Home" for the Jewish people in Palestine. None of the persons who had issued that declaration in 1917 were in power. Britain had meanwhile, reneged on their commitment to give Syria to the Arabs, in favor of their commitment to give Syria to France based on the Sykes Picot agreement. The Hashemites were no longer in power in Saudi Arabia either. The Mandate had created intense resentment, and riots had occurred in Palestine in 1920 and 1921. Motions were raised in both the House of Commons and the House of Lords to repeal the Balfour declaration. The motion was defeated in commons with the help of Churchill, Ormsby Gore and others, but it was felt that a compromise would be necessary. The "as implemented" mandate would be somewhat different from what the Zionists and the framers of the mandate had envisioned. Churchill, possibly with the help of Herbert Samuel, was given the thankless task of reframing the mandate in such a way that it would placate the Arabs, but still give Britain an excuse to keep Palestine from the French in the form of the "homeland for the Jewish people"
The British government decided to detach Palestine east of the Jordan river, constituting most of the area of Palestine, and form the Hashemite Kingdom of Transjordan, as shown in the map at right.
The White Paper of 1922, known as the "Churchill White Paper," or "Command Paper" alludes somewhat obliquely to this change. It affirms the right of Jews to a homeland in Palestine, refers to a Zionist resolution of 1921 declaring willingness to build the country in cooperation with the Arabs and notes:
When it is asked what is meant by the development of the Jewish National Home in Palestine, it may be answered that it is not the imposition of a Jewish nationality upon the inhabitants of Palestine as a whole, but the further development of the existing Jewish community, with the assistance of Jews in other parts of the world, in order that it may become a centre in which the Jewish people as a whole may take, on grounds of religion and race, an interest and a pride.
The White Paper attempts to resolve the various contradictory promises of the British Foreign office. The detachment of the eastern part of Palestine is said to satisfy both the provisions of the McMahon letter of 1915 to Sheriff Hussein, and also the wording of the Balfour declaration, which promised a Jewish National Home in Palestine, as opposed to a home encompassing all of Palestine. The White Paper also makes it clear that the Jews will not rule the Arabs in Palestine, but will only govern themselves, according to the then current British Foreign Office interpretation of the mandate. Churchill noted:
But in order that this community should have the best prospect of free development and provide a full opportunity for the Jewish people to display its capacities, it is essential that it should know that it is in Palestine as of right and not on the sufferance. That is the reason why it is necessary that the existence of a Jewish National Home in Palestine should be internationally guaranteed, and that it should be formally recognized to rest upon ancient historic connection.
This, then, is the interpretation which His Majesty's Government place upon the Declaration of 1917, and, so understood, the Secretary of State is of opinion that it does not contain or imply anything which need cause either alarm to the Arab population of Palestine or disappointment to the Jews.
The above is in conflict with the interpretation of Lloyd George, who had been Prime Minister when the Balfour Declaration was issued and with the interpretation of the American delegation to the Paris peace conference. Lloyd George wrote:
It was contemplated that when the time arrived for according representative institutions to Palestine, if the Jews had meanwhile responded to the opportunity afforded them by the idea of a National Home and had become a definite majority of the inhabitants, then Palestine would thus become a Jewish Commonwealth. (Memoirs, pp 736-7) (see the discussion in the introduction to the Balfour Declaration).
However, the winds of British policy had shifted, and Churchill's task was to justify the shift in yet another ambiguous document that could be interpreted in different ways to different people and at different times, or, in Churchill's words:
...the Secretary of State is of opinion that it does not contain or imply anything which need cause either alarm to the Arab population of Palestine or disappointment to the Jews.
However, the White paper contained a great many things that caused justifiable alarm to both sides, as the Arabs were not reassured that there would not be a Jewish-ruled entity in Palestine, and the Jews could see clearly the threat to partition Palestine and to limit immigration...