Considering the parable of the Persistent Widow (Luke 18:1-8), what central theological truth about prayer is Jesus emphasizing beyond simply not giving up?

A God only answers prayers that are repeated frequently. B God is unjust and needs to be worn down before he will act. C God's justice will ultimately prevail for those who cry out to him, even when it seems delayed or absent. D Prayer is primarily about changing God's mind rather than aligning our will with His.