The porter must be God the Father or the Spirit, the divine acceptance of the Son by the Father. God approves everything the Son does.
‘And the sheep hear his voice.’ It is happening to this day. There suddenly comes a time in your life. You are against God but perhaps you have been made to think. You cannot accept these things at first. You are full of doubts. You love this vain and passing world and yourself and your sin, and yet something is beginning to draw you and to draw at your heart. And then that day comes, that strange and mysterious day, when you just know this is real. You know that the call of God is true, that the Gospel is true. That we are a fallen race, that we are sinners, that we are unacceptable to a holy God. That he is a God who is there, the only explanation, the Creator of all, and suddenly you know it is true. There are still doubts, but now this has a demand upon you. Now you long for salvation, and you need Christ, and there is nothing more you want to know but that he has heard you, and he will respond to your repentance, and he has brought you to believe in him. Am I saved? It is the thing you most want. If somebody were to say to you – some person who ought to know – you are not saved, it would be crushing.