It is likely that this is based on some literal historical event. Just as the references to eye salve, to white clothing (as opposed to the black of the region), to riches, and to being lukewarm, relate to local circumstances, so in all probability does this knocking at the door.
First of all we apply this to ourselves as believers who are slipping backwards. If I am lukewarm, my devotions diminish. Have yours diminished? Have they become a perfunctory, almost formal exercise? If am I lukewarm my conscience becomes less active. Has your conscience gone quiet when it should warn you? Should you lose you temper or make excuses which are dishonest, or be unreasonable or selfish or lazy or covetous, does your conscience speak less loudly? That is lukewarmness. With lukewarmness, self-contentment takes over. Has that happened to any of us? Worldly and family matters now absorb us. Of course we have to live in this world, and we have duties to perform, and we have to be good parents and look after our families, and provide as best we can, but have worldly and earthly matters taken over, excluding spiritual things. Do we now think, ‘Oh, the church, and evangelistic effort and duties, are excessive. I do not have to be involved in them.’ Does attendance at services reduce down to two meetings a week, or even to one? Does TV take up more time? No sacrifices now for the Lord; only do manageable things. Christ and his word and his mission is no longer the centre of my conversation and my delight. That is being lukewarm, or it is beginning the descent into lukewarmness.
Can I be forgiven? Yes, because he uses this figure. Behold [See], I stand at the door.’ Believe that I will deal with you. I am at hand to save you. I am willing to save you, and, what is more, I am willing to save you immediately. All those elements are there: nearness, willingness, immediacy.
What must the seeker do? He must repent. He must trust him. But what else? He must throw open the door to accept his authority and yield to him. Pray to him: ‘Lord, I will do whatever thy word tells me to do. By thy help I will live for thee and thy standards, and serve thee and love thee first and foremost. Pardon my sin, bring my soul to life, give me a new nature, and I will be thine and give myself up to thee’, and he will come and he will accept you. You will know his grace, his pardoning love, and he will adopt you as his child, take you into the royal family of those who love the Lord. He will sup with you, have fellowship with you. He will deal with you day by day: hear you, bless you, guide you, and be yours, all by grace. All this will come by repentance, by belief, by yielding, by submission.