Verse 20: Behold, (Cant. 5:2) I stand at the door, and knock: (Luke 12:37) if any man hear my voice, and open the door, (John 14:23) I will come in to him, and will sup with him, and he with me.
[Behold, I stand (the Preterit tense, ἕστηκα, in the place of the Present, after the fashion of the Hebrews [Piscator] [as the following κρούω, I knock, indicates]) at the door (namely, of thy heart [Tirinus, Cluverus, Pareus, thus Ribera, Menochius], that is, at thy understanding and will [Tirinus]: This shows both the patience of Christ, and their ingratitude [Durham]) and knock] By repeated illuminations, and stirrings internal and external (Tirinus). To knock is to seek admission by the words of internal inspirations (Ribera, Menochius). Christ knocks both externally, by the preaching of the Law and Gospel, and by the sending of crosses and afflictions; and internally, by grace illuminating minds and opening hearts, etc. (Pareus). It shows that Christ does this solicitously and importunately (Durham). Lest perchance he despair that Christ is going to be favorably inclined to him, or that he is able to return to his former state, He says, Behold, I stand, etc. (Ribera); that is to say, Even if I be shut out by thee (Ribera, Menochius, similarly Tirinus), through indolence and other sins (Tirinus), I shall return unto thee again with a zeal for thy salvation; and I beat the door, like a guest, so that thou mightest open to me (Ribera, Menochius). Your hearts, closed to me as savior, I do not pass by; I do not sit by idle or languid; but I stand unwearied and knock, so that I might rouse those things asleep, etc. (Cluverus). He returns to the Door, but in another sense, just as the similitude of a Shepherd is variously used in John 10. But someone might say, Why would He, who holds the key, knock? I say, Because a bolt was fastened to the door, which must be removed. This bolt is the habit of sin (Grotius).
[If any man (of whatsoever sort he be, sinner, hypocrite, one that for a long time has resisted the Gospel, etc. [Durham]) hear my voice] For those who knock are wont at the same time to cry out, Open, as in the Comedies. Both calling out here and knocking signify Thoughts instilled by God for warning the conscience of the sinner. God does this for awhile, but not forever. For He hardens many that are obstinate to Him (Grotius). If he hear, that is, by faith embrace the conditions of the covenant of grace offered to him, out of a comparison with Isaiah 55:2, 3, which also is understood by the following opening by a comparison with Psalm 81:11, 13 and Acts 16:14 (Durham).
[And open, etc.] That is, If he admit saving admonitions (Ribera, Menochius).
[I will come in to him (as a guest [Ribera, Menochius], as unto a most gracious host [Tirinus]: There will be a union between me and him [Durham]: Christ enters when He grants His Spirit [Grotius]; or, where through faith He insinuates Himself into our hearts [Pareus]), and will eat with him (that is, forgetful of injuries and rejection [Ribera, Menochius]; I will live in a friendly and familiar manner with him [Ribera, Menochius, similarly Camerarius, Piscator, Tirinus, Durham]; I will pleasantly delight myself with him [Tirinus], and I will accept his services [Ribera, Menochius]; I will communicate myself to him in the word and Sacraments by faith, removing sins, healing infirmities, delighted by his faith and conversion [Pareus]), and he with me] Understand, will eat (Pareus). He speaks as a guest (Ribera, Menochius), yet not empty-handed nor unwelcome (Pareus), but greater and wealthier (Ribera, Menochius, Pareus); who, coming into the home of another rather gives than receives benefit (Ribera, Menochius), and He repays to him the sumptuous fare, which things here are the heavenly goods of the Gospel, righteousness, holiness, peace, etc. (Pareus). It indicates the complete joy of the sinner in his union and communion with Christ (Durham). It is a great honor to have a King as a guest. Now, by a banquet is understood Joy, both Christ’s on account of the converted sinner, and the converted sinner’s on account of Christ living in him. For great delights are wont to be expressed under the similitude of Feasts, Luke 12:37; 15:23 (Grotius). Hence Interpreters rightly gather that God is not preceded by the free will of men, but precedes by His stirring grace; likewise others add that man is able to reject the offered grace, or to receive it, which is false (Cluverus). Now, it is to be observed that Sacred Scripture speaks of our conversion in two ways, and attribes the whole of conversion sometimes to us and to our will, as here, and in Ezekiel 18:31; Zechariah 1:3; and that in such a way that it might stir our wills, and pour into our spirit strength for fulfilling: sometimes to Himself and to His grace, as in Jeremiah 31:18; Ezekiel 36:26, 27; John 6:44; 15:5 (Pareus). But, with the matter well considered, the same thing appears to be signified here as in Matthew 24:43, 44, etc., where by a similitude of a servant being vigilant against the coming of his Lord, so that he might open to him, Christ exhorts all the faithful to be ever vigilant and prepared to recline and eat with Him, that is, to enjoy eternal gladness. Thus in this place, Behold, I stand, that is, now I will come for judgment, being about to knock on the door. If he hear…I will come in to him, etc., namely, into my house, in which my servant was keeping vigil; and I will invite him to my supper, that is, he will be a sharer in my joys and goods. Therefore, this place makes nothing for the grace of God, knocking, and waiting, and depending as far as effect upon our acceptation, which grace sound doctrine does not receive; for, that God is He who opens the will, teaches Augustine, etc. (Estius).
Behold, etc.:There is a double interpretation of this text, each of them claiming under very valuable interpreters; some making it a declaration of Christ’s readiness to come in to souls, and to give them a spiritual fellowship and communion with himself; others interpreting it of Christ’s readiness to come to the last judgment, and to take his saints into an eternal joyful fellowship and communion with himself: hence there is a different interpretation of every sentence in the text. I stand at the door; either, in my gospel dispensations, I stand at the door of sinners’ hearts; or, I am ready to come to judge the world. And knock, by the inward monitions and impressions of my Spirit, or my ministers more externally; or, I am about to knock, that is, I am ready to have the last trump sounded. If any man hear my voice,and open the door; that is, if any man will hearken to the counsels and exhortations of my ministers, and to the monitions of my Spirit, and not resist my Holy Spirit; or, if any man hath heard my voice, and opened his heart to me. I will come in to him; I will come in by my Spirit, and all the saving influences of my grace; or, I will come to him as a Judge to acquit him. And will sup with him, and he with me; and I will have a communion with him in this life, he shall eat my flesh, and drink my blood; or, I will have an eternal fellowship and communion with him in my glory. The phrase seems rather to favour the first sense; the so frequent mention before of Christ’s coming to judgment, and the reward of another life, as arguments to persuade the angels of the churches to their duty, favours the latter sense.
 Greek: ἰδού, ἕστηκα ἐπὶ τὴν θύραν καὶ κρούω· ἐάν τις ἀκούσῃ τῆς φωνῆς μου, καὶ ἀνοίξῃ τὴν θύραν, εἰσελεύσομαι πρὸς αὐτόν, καὶ δειπνήσω μετ᾽ αὐτοῦ, καὶ αὐτὸς μετ᾽ ἐμοῦ.  Ἕστηκα is a Perfect form of ἵστημι. The Perfect tense often conveys a Present sense.  In the Present tense.