Why did Henry VIII listen to Martin Luther's ideas?

At first, Henry was a religious conservative, siding with Rome, who dismissed Martin Luther's ideas out of hand. Henry felt so strongly opinionated about this that by1518 he hd started to write a book in defense of the papacy while he was reading Martin Luther's attack on indulgences. This book eventually developed into the "Assertio Septem Sacramentorum" or Defence of the Seven Sacraments, which defended the the supremacy of the Pope (and ironically, the sacramental nature of marriage). In 1521, as a result of this spiriited defense, Pope Leo X awarded Henry the title of "Fidei defensor" a Latin title which translates as "Defender of the Faith" and is still used by English monarchs today.

However, by 1525, motivated by his obsession with obtaining a male heir, and strongly enamored of Anne Boleyn, Henry was desperate to find a solution to allow him to put aside Catherine of Aragon, his Queen since 1509, in favor of someone who would give him a live male heir. By this point, Henry was seriously considering Luther's ideas on the independence of church and state, as a lever clearing the way for him as King, to rule on, and invalidate his current marriage. This obsession led finally in 1534, to the Act of Supremacy which declared that the King was "the only Supreme Head in Earth of the Church of England" and the Treasons Act 1534 made it high treason, punishable by death, to refuse to acknowledge the King as such.

Though mainly motivated by dynastic and personal concerns, and despite never really abandoning the fundamentals of the Roman Catholic Church, Henry ensured that the greatest act of his reign would be one of the most radical and decisive of any English monarch. His break with Rome in 1533-34 was an act with enormous consequences for the subsequent course of English history beyond the Tudor dynasty.