It is briefly given in Luke 13:24 (last clause), and both parts of the reason there are expanded in the following verses. Effort is needed for entrance, because many are shut out. The questioner would be no better for knowing whether few would enter, but he and all need to burn in on their minds that many will not.
Very solemnly significant is the difference between striving and seeking. It is like the difference between wishing and willing. There may be a seeking which has no real earnestness in it, and is not sufficiently determined, to do what is needful in order to find. Plenty of people would like to possess earthly good, but cannot brace themselves to needful work and sacrifice. Plenty would like to go to heaven,' as they understand the phrase, but cannot screw themselves to the surrender of self and the world. Vagrant, halfhearted seeking, such as one sees many examples of, will never win anything, either in this world or in the other. We must strive, and not only seek.
That is true, even if we do not look beyond time; but Jesus carries our awed vision onwards to the end of the days, in the expansion of his warning, which follows in Luke 13:25-27. No doubt, the words had a meaning for His hearers in reference to the Messianic kingdom, and a fulfilment in the rejection of the nation. But we have to discern in them a further and future significance.
Observe that the scene suggested differs from the similar parable of the virgins waiting for their Lord, in that it does not describe a wedding feast. Here it is a householder already in his house, and, at the close of the day, locking up for the night. Some of his servants have not returned in time, have not come in through the narrow gate, which is now not only narrow, but closed by the master's own hand. The translation of that is that, by a decisive act of Christ's in the future, the time for entrance will be ended. As in reference to each stage of life, specific opportunities are given in it for securing specific results, and these can never be recovered if the stage is past; so mortal life, as a whole, is the time for entrance, and if it is not used for that purpose, entrance is impossible. If the youth will not learn, the man will be ignorant. If the sluggard will not plough because the weather is cold, he will beg in harvest.' If we do not strive to enter at the gate, it is vain to seek entrance when the Master's own hand has barred it.
The language of our Lord here seems to shut us up to the conclusion that life is the time in which we can gain our entrance. It is no kindness to suggest that perhaps He does not shut the door quite fast. We know, at all events, that it is wide open now.
The words put into the mouths of the excluded sufficiently define their characters, and the reasons why they sought in vain. Why did they want to be in? Because they wished to get out of the cold darkness into the warm light of the bountiful house. But they neither knew the conditions of entrance nor had they any desire after the true blessings within. Their deficiencies are plainly marked in their pleas for admission. At first, they simply ask for entrance, as if thinking that to wish was to have. Then, when the Householder says that He knows nothing about them, and cannot let strangers in, they plead as their qualification that they had eaten and drunk in His presence, and that He had taught in their streets. In these words, the relations of Christ's contemporaries are described, and their immediate application to them is plain.
Outward connection with Jesus gave no claim to share in His kingdom. We have to learn the lesson which we who live amidst a widely diffused, professing Christianity sadly need. No outward connection with Christ, in Christian ordinances or profession, will avail to establish a claim to have the door opened for us. A man may be a most respectable and respected church-member, and have listened to Christian teaching all his days, and have in life a vague wish to be saved,' and yet be hopelessly unfit to enter, and therefore irremediably shut out.
The Householder's answer, in its severity and calmness, indicates the inflexible impossibility of opening to such seekers. It puts stress on two things--the absence of any vital relationship between Him and them, and their moral character. He knows nothing about them, and not to be known by the Master of the house is necessarily to be shut out from His household. They are known of the Shepherd who know Him and hear His voice. They who are not must stay in the desert. Such mutual knowledge is the basis of all righteousness, and righteousness is the essential condition of entrance.
These seekers are represented as still working iniquity. They had not changed their moral nature. They wished to enter heaven, but they still loved evil. How could they come in, even if the door had been open? Let us learn that, while faith is the door, without holiness no man shall see the Lord. The worker of iniquity has only an outward relation to Jesus. Inwardly he is separated from Him, and, at last, the outward relation will be adjusted to the inward, and departure from Him will be inevitable, and that is ruin.