Just as we should ask for what we desire from God and seek after Him, we should knock on the door leading to the treasures He has for us and it will be opened.

Luke 11:10 For everyone who asks receives, and the one who seeks finds, and to the one who knocks it will be opened.

In this world and with people you have to knock till your knuckles are raw in some cases, but Jesus says that our Heavenly Father is not like that! He does not hold out on us and as an example wants above all things to give us His Holy Spirit. He wants what's good for us to come to us often more than we do!

In Luke 18 Jesus gives the parable of the persistent widow and shows how in this age and with people we may have to keep knocking on the door to get justice and help, but not with God.

Luke 18:7 And will not God give justice to his elect, who cry to him day and night? Will he delay long over them? 8 I tell you, he will give justice to them speedily.

That's the kind of God that we worship. He answers us speedily.
He's a GOOD God.

So why does the scripture suggest in the original language that we should "knock and keep on knocking"?

May I suggest it's not that God can be slow to answer sometimes, but that we live in a world with another god and this god and his minnions can delay the reception of what we ask for. So we should not give up, but in faith keep on knocking/praying.

This is illustrated in the life of Daniel, a great man of God. Daniel had started praying to God regarding a particular situation but it was three weeks later before an angel turned up to give Daniel the answer. And when he did, this is what the angel said...

Dan 10:12-14 Then he continued, “Do not be afraid, Daniel. Since the first day that you set your mind to gain understanding and to humble yourself before your God, your words were heard, and I have come in response to them. But the prince of the Persian kingdom resisted me twenty-one days. Then Michael, one of the chief princes, came to help me, because I was detained there with the king of Persia. Now I have come to explain to you what will happen to your people in the future, for the vision concerns a time yet to come.”

You see here that the angel was dispatched straight away to bring Daniel the answer, but Satan delayed him for three weeks until Michael, an Archangel came to his aid and he was released to go on his way!

There is a spiritual battle going on around us and we must at times pray through fervently for our answer. It's on it's way. Never give up!