He told them a parable to illustrate that it is necessary always to pray and not lose heart.
What happens when you move far away from your family and don’t communicate by calling them? Your relationship with them will grow cold to the point that it will die. Your feelings will start to dwindle by not thinking about them or remembering the good memories that you once had together and eventually it won’t bother you if you never heard from them again. That’s the danger we face if we don’t have a prayer life with the Lord. You cannot sustain your Christian walk without feeding your soul God’s Word and prayer, both are two sides of the same coin which you cannot do one without the other.