[b]Act 2:1-47[/b] -
Chapter 2 relates the fulfilment of this promise, in answer to the spirit of dependence manifested in their united prayers.
The Spirit comes from above, in His own power, to possess and fill the dwelling-place prepared for Him.
This event, important beyond all others with respect to man's condition here below, has here a very simple character, because there is no question of the causes of this marvellous gift, of the work on which it depends, of the glory with which it is connected and which it reveals, and of which it is the earnest: we have here only the fact of its power. The disciples "were endued with power from on high."
The form of its appearance, however, is characteristic. On Jesus the Holy Ghost descended in the shape of a dove, because He was not to make His voice heard in the streets, nor break the bruised reed, nor quench the smoking flax. But here it was the power of God in testimony, the word; which was like consuming fire, judging all that came before it. Nevertheless it was in grace, and was to go beyond the narrow limits of Jewish ordinances to proclaim the wonderful works of God to every tongue and nation under the sun. It was that mighty wind from heaven, which manifested itself to the disciples, and came upon them in the form of tongues of fire, each one divided into several. This marvel attracts the multitude; and the reality of this divine work is proved by the fact that persons from numerous countries hear these poor Galileans proclaim to them the wonderful works of God, each one in the language of the country whence he came up to Jerusalem. 
The Jews, who did not understand these languages, mock; and Peter declares to them in their own tongue, and according to their own prophecies, the true character of that which had taken place. He takes his stand upon the resurrection of Christ, foretold by the prophet-king, and upon His exaltation by the right hand of God. This Jesus, whom they had crucified, had there received the promise of the Father, and shed forth that which produced the effects that they heard and saw. They were therefore to know assuredly, that God had made that same Jesus whom they had rejected both Lord and Christ.
The character of this testimony will be remarked here. It is essentially that of Peter. It goes no farther than the affirmation of the fact, that He who had been rejected by the Jews is made in heaven Lord and Christ. It begins with Jesus known of the Jews on earth, and establishes the truth of His being raised again, and exalted to the position of Lord. God has done this. The apostle does not even proclaim Him as the Son of God. We shall see that, if it is not done by Peter in the Acts, Paul on the contrary does it from the first moment of his conversion. Peter states the result at that moment in power, and does not speak of the kingdom. He only reminds them that the Spirit was promised in the last days, and alludes to the terrible day of the coming judgment, which would be preceded by alarming signs and wonders. Without speaking of the fulfilment of the promise of the kingdom, the time of which the Father had kept secret, he puts the fact of the gift of the Holy Ghost in connection with the responsibility of Israel, to whom God still acted in grace, by preaching to them a glorified Christ, and by giving them proofs of His glory in the gift of the Holy Ghost, made sensible to all. This is the presence of the Holy Ghost according to Joh_15:26-27. The testimony as a whole, however, is founded on and carries out the mission of Luke 24. Only in Luke we have nothing of baptism. See Luk_24:47-49, to which this fully corresponds. The testimony was addressed to the Jews; nevertheless it was not confined to them,  and it was
separative. "Separate yourselves from this untoward generation." This separation was founded on a real and moral work "repent": the past was all to be judged, and publicly demonstrated by their reception amongst Christians by baptism, in order to receive the remission of their sins, and participate in this heavenly gift of the Holy Ghost. "Repent, and be baptised every one of you in the name of Jesus Christ, for the remission of sins, and ye shall receive the gift of the Holy Ghost." This work is individual. There was judgment on all the past, the admission amongst them by baptism, and the consequent participation in the Holy Ghost, who dwelt where they came. We see at once the difference between the moral change already wrought, the repentance which their godly sorrow works, and the reception of the Holy Ghost. This was consequent on the remission of their sins to which they were brought. This gift depended in a regular way on their admission amongst Christians, the house where He dwelt, built in the name of Jesus. Afterwards the promise is declared to belong to them and to their children to the house of Israel as such to them and to their children after them. But it went beyond the limits of God's ancient people. The promise was also to those that were afar off; for it was fulfilled, in connection with faith in Christ, to all who through grace should come into the new house all whom the Lord, the God of Israel, should call. The call of God characterised the blessing. Israel, with her children, was owned, but a remnant called out from among them. The Gentiles, being called, shared the blessing.
The result of this ineffable gift is related to us. It was not merely a moral change, but a power which set aside all the motives that individualised those who had received it, by uniting them as one soul and in one mind. They continued steadfastly in the apostles' doctrine; they were in communion with each other and the apostles; they broke bread; they spent their time in prayer. The sense of God's presence was powerful among them; and many signs and wonders were wrought by the hands of the apostles. They were united in the closest bonds; no man called anything his own, but all divided their possessions with those that needed. They were daily in the temple, the public resort of Israel for religious exercises, whilst having their own apart breaking bread at home daily. They ate with joy and gladness of heart, praising God, and having favour with all the people around them.
Thus the assembly was formed; and the Lord added to it daily the remnant of Israel, who were to be saved from the judgments that should fall on a nation which had rejected the Son of God, their Messiah; and, thank God, from yet deeper ruin. God brought into the assembly thus owned of Him by the presence of the Holy Ghost those whom He spared in Israel.  A new order of things had commenced, marked by the presence of the Holy Ghost.  Here was found the presence and the house of God, although the old order of things still existed until the execution of judgment upon it.
The assembly was formed therefore by the power of the Holy Ghost come down from heaven, on the testimony that Jesus, who had been rejected, was raised up to heaven, being made of God both Lord and Christ. It was composed of the Jewish remnant who were to be spared, with the reserve of bringing in Gentiles whenever God should call them. It was as yet formed in connection with Israel in the patience of God, yet apart in power, God's dwelling place.
The rationalistic notion that it was a kind of excited gibberish, just as the unbelieving Jews thought, is absurd beyond conception. Think of Paul's thanking God that he spoke more kinds of gibberish than they all, and God giving a gift for interpreting gibberish!
The testimony is in terms which, applying to Jews there and scattered abroad, yet opened the door to the Gentiles in the sovereignty of God "all that are afar off, as many as the Lord our God shall call." God is still the God of man; but He calls whom He pleases.
This is the force of ('soozomenos') "those that were to be saved," Act_2:47.
God never dwelt with man but on the ground of redemption, not with Adam nor Abraham. Compare Exo_29:46.
John Darby's Synopsis