Background: Elizabeth of York (11 February 1466 - 11 February 1503) was queen consort of England from 1486 until her death. As the wife of Henry VII, she was the first Tudor queen. She was the daughter of Edward IV and niece of Richard III, and she married the king following Henry's victory at the Battle of Bosworth which started the last phase of the Wars of the Roses. She was the mother of King Henry VIII.
Context: As the eldest daughter of Edward IV with no surviving brothers, Elizabeth of York had a strong claim to the throne in her own right, but she did not assume the throne as queen regnant. Such a precedent would not truly come to England for another 67 years, when her granddaughter, Mary I, acceded to the throne. Though initially reluctant to keep his promise Henry VII acknowledged the necessity of marrying Elizabeth of York to ensure the stability of his rule and weaken the claims of other surviving members of the House of York, but he ruled in his own right and claimed the throne by right of conquest and not by his marriage to the heir of the House of York. He had no intention of sharing power. He consequently chose to be crowned on 30 October 1485 before his marriage.  Henry VII had the Titulus Regius repealed, thereby legitimising the children of Edward IV, and acknowledged Edward V as his predecessor. After procuring papal dispensation, Cardinal Bourchier, Archbishop of Canterbury, officiated at the wedding of Henry VII and Elizabeth of York on 18 January 1486 in Westminster Abbey. Their first son, Arthur, was born on 20 September 1486. Elizabeth of York was crowned queen on 25 November 1487. Following her coronation, she gave birth to seven more children, but only four survived infancy: Arthur, Margaret, Henry and Mary.  Despite being a political arrangement at first, the marriage proved successful and both partners appear to have grown to love each other. Elizabeth of York did not exercise much political influence as queen due to her strong-minded mother-in-law Lady Margaret Beaufort, but she was reported to be gentle, kind, and generous to her relations, servants, and benefactors. When not at official gatherings, she lived a quiet life largely away from politics with three of her children at Eltham Palace. Elizabeth of York enjoyed music and dancing as well as dicing. She also kept greyhounds.  On 14 November 1501, Elizabeth of York's 15-year-old son Arthur married Catherine of Aragon, daughter of King Ferdinand II of Aragon and Queen Isabella I of Castile. The pair were sent to Ludlow Castle, the traditional residence of the prince of Wales. Arthur died in April 1502. The news of Arthur's death caused Henry VII to break down in grief, as much in fear for his dynasty as in mourning for his son. Elizabeth comforted him, telling him that he was the only child of his mother but had survived to become king, that God had left him with a son and two daughters, and that they were both young enough to have more children.
Question: Why was it necessary?

Answer:
to ensure the stability of his rule and weaken the claims of other surviving members of the House of York,