Summary: Expanding the Kingdom of God during this Church Age is a mandate that is still incumbent upon all churches. If the doors to continued expansion are closing, it may be because we are disobedient, or it may presage the closing of this present age.
“To the angel of the church in Philadelphia write: ‘The words of the holy one, the true one, who has the key of David, who opens and no one will shut, who shuts and no one opens.
“‘I know your works. Behold, I have set before you an open door, which no one is able to shut. I know that you have but little power, and yet you have kept my word and have not denied my name. Behold, I will make those of the synagogue of Satan who say that they are Jews and are not, but lie—behold, I will make them come and bow down before your feet, and they will learn that I have loved you. Because you have kept my word about patient endurance, I will keep you from the hour of trial that is coming on the whole world, to try those who dwell on the earth. I am coming soon. Hold fast what you have, so that no one may seize your crown. The one who conquers, I will make him a pillar in the temple of my God. Never shall he go out of it, and I will write on him the name of my God, and the name of the city of my God, the new Jerusalem, which comes down from my God out of heaven, and my own new name. He who has an ear, let him hear what the Spirit says to the churches.’” 
The Eighteenth through the Twentieth Centuries witnessed decades of rapid expansion for the Faith. As evangelicalism flexed long dormant spiritual muscles, the boundaries of the Faith were pushed beyond anything experienced since the days of the Apostles. The names of missionaries so greatly admired in modern church literature were quite often men and women who laboured throughout the two millennia concluding with the first half of the Twentieth Century. Without question, these were glorious days for the Faith. Not since the days of the Apostles had the Faith penetrated so deeply into territories Satan had long dominated. I fear, however, that the expansion witnessed throughout that period is now drawing to a close.
British Foreign Secretary Sir Edward Grey stood in the window of his room in the Foreign Office. It was getting dusk, and the lamps were being lit in the space below on which he was looking. A friend standing with him heard Grey remark, “The lamps are going out all over Europe; we shall not see them lit again in our life-time.”  I sense a somewhat similar sentiment as I cast my gaze over the church era now passing and as we step boldly into this brave, new era.
I am not negative in saying this, though I have serious doubts about the spiritual vigour of contemporary Christendom, regardless of how popular the Faith may appear at this moment. My confidence does not rest in the churches, but in the Risen Lord Who is Head of the churches. The rapid expansion of the previous era serves to encourage us as we read of men and women imbued with faith and courage that cannot be accounted for without appeal to the Spirit of God.
I am not suggesting that we are to live in the memory of the glory days of the past, but it is reasonable to remember that those who preceded us were men and women of great faith. Convinced that God was leading as they advanced into darkened regions, they were prepared to labour to ensure that the Faith was established throughout the world. The vast majority of major missionary organisations were established during this period, though many no longer vigorously pursue the goals that first marked their labours among the churches.
I do not recommend that we again fight denominational battles such as those fought when gifted spokesmen of the Faith stood firm for the Fundamentals of the Faith against the rot of modernism that infected a majority of numerous Christian organisations in the western world. Neither do I suggest that those who hear form a committee to organise reoccupying some of the great old church buildings that once dotted the land. Those days are fading rapidly, if they are not gone entirely. I do recommend that we recapture the zeal of those earlier saints, if perchance the Lord would employ us to His glory in these waning days of the Church Age. In order to pursue this goal, I look at the words of the Risen Son of God to the congregation in Philadelphia.
EXPANSION COMMANDED — “I know your works. Behold, I have set before you an open door, which no one is able to shut. I know that you have but little power, and yet you have kept my word and have not denied my name. Behold, I will make those of the synagogue of Satan who say that they are Jews and are not, but lie—behold, I will make them come and bow down before your feet, and they will learn that I have loved you” [REVELATION 3:8-9].