‘And the angel whom I saw standing on the sea and on the earth lifted up his right hand to Heaven and swore by him who lives for ever and ever, who created the heaven and the things that are in it, and the earth and the things that are in it, and the sea and the things that are in it, that there shall no longer be delay. But in the days of the voice of the seventh angel, when he is about to sound, then is finished the mystery of God, according to the good tidings which he declared to his servants the prophets.'
Compare the man clothed in linen in Daniel 12:7 who raises both right hand and left hand and swears by Him Who lives for ever. He too forecasts the end. So the hardness of men's hearts means that God will no longer delay. God's longsuffering is now at an end (2 Peter 3:9). He Who lives for ever and ever and created all things, to whom vast ages are but a trifle, will wait no longer. The angel's stance is itself a declaration of the final takeover. All of heaven, earth and sea belongs to the God Who created it, and now He will take possession of His own.
The mention of the mystery of God revealed to the prophets brings to mind the words of Amos, ‘surely the Lord will do nothing unless he reveals his secret to his servants the prophets' (Amos 3:7). God had revealed to the Old Testament prophets what he would do, but it was in veiled form for they could not have understood the whole, it was a ‘mystery' to be more fully revealed. They knew it would be glorious. They knew it would bring in the triumph of God. They were aware of it as ‘good tidings' but they were not fully aware of the implications.
It was a mystery which Jesus Christ, the greatest Prophet of all, and the great New Testament prophets, Paul and the other Apostles and prophets, were able to more fully reveal in their proclamation of ‘the good tidings of the Gospel'. (The early church saw prophecy as continued in their midst). As Paul puts it ‘Now to him who is able to establish you in accordance with my Gospel and the preaching of Jesus Christ, in accordance with the revelation of the mystery, which has been kept in silence through times eternal but is now made clear and open, even by means of the Scriptures of the prophets, according to the commandment of the Eternal God' (Romans 16:25-26). What they revealed of what the earlier prophets originally declared will now be brought to completion.
‘There will be time (or delay) no longer.' No longer time is to be allowed. God has reached the end of His longsuffering. Thus there will no longer be delay.