The last two letters describe the last two of the seven ages. Philadelphia follows the Sardis age, in which Luther brought what he found in the Scriptures to the people. Laodicea is the age we live in.
Philadelphia: the open door
Christ introduces himself to Philadelphia as holy and true, the One with the key of David, who opens what no one can shut, and he sets before them an open door.
That door is the Scriptures reaching ordinary people. Printing had just been invented, about 1440, and the Bible was among the first things printed. Printing houses took time to set up, but then Bibles came into people's hands and teachers of Scripture became available. People read, thought and formed convictions of their own.
John Calvin and John Knox, who lived in Luther's time, taught predestination and eternal security, and people misread both. Predestination was taken to mean that God has already marked each person for destruction or for salvation. But God gave everyone free will and forces no one. In his foreknowledge he saw what each would choose, and in human language we say he wrote it down. The writing does not cause the choice. Eternal security rests on Jesus' word that whoever believes in him will not perish, yet some concluded that, having believed and been baptised, they might do as they pleased. Both teachings became excuses for sin. Meanwhile followers of Luther became Lutherans, followers of Calvin and Knox became Presbyterians, and Baptists and other groups formed as well.
Wesley and holy living
About 1750 John Wesley began preaching in England, village to village, with few followers at first. Knowing these teachings, he said that sanctification, or holy living, is still needed. This is why Christ calls himself holy.
Sanctification has two senses. First, when you believe, repent and are baptised, your sins are forgiven and on the day of judgement you are counted holy, not guilty. Second, after baptism you keep correcting your way, day by day, by what you learn from God's word; if you never do, you took baptism in vain, because you did not truly repent. Before Wesley many thought holiness meant going to church in clean white clothes, but holy and sinner are opposites. Wesley taught what to do and not to do, with a method, and so his followers were called Methodists.
At first no church invited him; later the same people welcomed him. From 1750 to nearly 1900 his teaching spread through the English church, and many from other churches, even Roman Catholics, joined the Methodists. This is how those who opposed came and bowed at the feet of the faithful.
The overcomer will be a pillar in God's temple: a pillar supports a building, and those who teach the church from Scripture how to live support it, because others walk on their teaching. Christ also promises to keep Philadelphia from the hour of trial coming on the whole world. The Philadelphian age ended in 1906; Laodicea follows, and then the great tribulation, which the Lord will not bring them into.
Laodicea: the lukewarm age
Laodicea, the seventh age, began in 1906, and we live in it. Christ calls himself the Amen, the faithful and true witness, and the beginning of God's creation. Faithfulness is stressed because it is fading: a generation or two ago people kept their word, but now it is common to say, I never said that, or, do you have proof?
They are neither cold nor hot. A generation or two ago, Protestants and Catholics did not even marry, and Lutherans, Calvinists and Methodists kept no ties with the older churches. Now everything is mixed. Infant baptism is fine, adult immersion is fine, and either way baptism has happened. No one searches for what is actually true: it is still God's name, so what difference does it make? A spirit of compromise is at work. The Lord would rather we say that what is true is true and what is false is false.
They also say, I am rich and need nothing: each person thinks he knows everything and has nothing to learn. The Lord says they are wretched, miserable, poor, blind and naked, and do not know it.
Gold, white clothing and eye salve
He counsels them to buy from him gold tried in the fire, white clothing and eye salve. These are not sold in a shop; Scripture shows what they mean.
White clothing has two parts.
…he hath clothed me with the garments of salvation, he hath covered me with the robe of righteousness…
— Isaiah 61:10
The garments of salvation are received when you believe, repent and are baptised and so are forgiven. The robe of righteousness is the righteous life lived after repentance. In a world full of wrong this is hard and will bring trouble, but he calls for it.
Gold tried in the fire is faith that has passed the test; Peter says the testing of faith is worth more than gold that perishes (1 Peter 1:7). Eye salve is understanding prophecy: here "seeing" means knowing what is to come. We see the visible world well enough; we need to understand God's things still ahead.
The door and the throne
Those the Lord loves he rebukes and disciplines.
Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me.
— Revelation 3:20
The meal is God's word, for we live not by bread alone but by his word. If we open our hearts we shall learn and understand it; if we refuse to learn, we shall not receive it. The overcomer is promised a place with Christ on his throne, which means holding authority as a king does, not sitting on a seat somewhere in heaven.
The seven letters picture seven ages inside the age of grace, nearly two thousand years. When the seventh ends, the age of grace ends and Daniel's seventieth "seven" (saptak) begins. We live in the last age, which will end soon.
Takeaway
Take the Lord's counsel for our own age: be saved and live righteously, let your faith be tested like gold, and understand the prophecies. Do not settle into compromise or think you already know everything. Open the door to Christ and learn his word.