The answer
Christ, the Good Shepherd, in His customary meekness stands at the door knocking. One person chooses to open the door (the stubborn door of the heart) and Christ enters and pours His grace upon it enlightening it and casting out its darkness. Another person refuses to open the door, and rather barricades himself in deeper darkness. That door is hardened by the ceasing of God's knocking grace upon it. A door symbolizes the separation of what is on the inside from what is on the outside. If one chooses to keep God outside, God will not impose Himself, granting that the same door remains shut (hardened). Lydia had heard St. Paul, accompanied by St. Luke, as they spoke to the women gathered in that place. Although she had a trade which brought her good wages, she "worshipped God." (Therefore she was willing to hear Christ knocking at the door of her heart.) "The Lord opened her heart to heed the things spoken of by Paul" and she subsequently had her household baptized; and invited God's servants in her home. Pharoah, surely had many more opportunities than Lydia to witness God's might and power. In the Old Testament, in spite of the miracles and plagues, Pharoah exhibited an irresponsive heart. So, God used Pharoah's already hard and insensitive heart, hardening it even more, to prove His love for His people; and desire to rescue and redeem them by His own hand.Answered by His Eminence Metropolitan Youssef (opens in a new tab)