At its core the basis for understanding where the church is during the tribulation period is based on a literal understanding of scripture. (If you do not understand the dynamics of the understanding then its best not to try and misapply it to other verses that have specific genre that use parabolic or parables etc.)
Second, it is based on understanding the nature of the tribulation period and if that nature is contrary to God's will for the church. For example, Paul wrote that 1Th 5:9 For God has not destined us for wrath, but to obtain salvation through our Lord Jesus Christ,.
The Book of Revelation itself describes this time as the wrath of God:
Rev 6:16 calling to the mountains and rocks, “Fall on us and hide us from the face of him who is seated on the throne, and from the wrath of the Lamb,
Rev 6:17 for the great day of their wrath has come, and who can stand?”
Rev 11:18 The nations raged, but your wrath came, and the time for the dead to be judged, and for rewarding your servants, the prophets and saints, and those who fear your name, both small and great, and for destroying the destroyers of the earth.”
Rev 12:12 Therefore, rejoice, O heavens and you who dwell in them! But woe to you, O earth and sea, for the devil has come down to you in great wrath, because he knows that his time is short!”
Rev 14:10 he also will drink the wine of God's wrath, poured full strength into the cup of his anger, and he will be tormented with fire and sulfur in the presence of the holy angels and in the presence of the Lamb.
Rev 14:19 So the angel swung his sickle across the earth and gathered the grape harvest of the earth and threw it into the great winepress of the wrath of God.
Rev 15:1 Then I saw another sign in heaven, great and amazing, seven angels with seven plagues, which are the last, for with them the wrath of God is finished.
Rev 15:7 And one of the four living creatures gave to the seven angels seven golden bowls full of the wrath of God who lives forever and ever,
Rev 16:1 Then I heard a loud voice from the temple telling the seven angels, “Go and pour out on the earth the seven bowls of the wrath of God.”
Rev 16:19 The great city was split into three parts, and the cities of the nations fell, and God remembered Babylon the great, to make her drain the cup of the wine of the fury of his wrath.
Rev 19:15 From his mouth comes a sharp sword with which to strike down the nations, and he will rule them with a rod of iron. He will tread the winepress of the fury of the wrath of God the Almighty.
Also there is a clear distinction in scripture between national Israel and the church. It is true that believing Jews, during the church age, are part of the church but that is not evidence that God is done with National Israel and no where in scripture does God suggest that He is. In fact in Romans Paul makes it clear that he is not when he says:
Rom 11:25 Lest you be wise in your own sight, I do not want you to be unaware of this mystery, brothers: a partial hardening has come upon Israel, until the fullness of the Gentiles has come in.
Rom 11:26 And in this way all Israel will be saved, as it is written, “The Deliverer will come from Zion, he will banish ungodliness from Jacob”;
Rom 11:27 “and this will be my covenant with them when I take away their sins.”
Rom 11:28 As regards the gospel, they are enemies for your sake. But as regards election, they are beloved for the sake of their forefathers.
Rom 11:29 For the gifts and the calling of God are irrevocable.
The fulness of the Gentiles is the church age. It is what Paul was called to begin:
Act 13:46 And Paul and Barnabas spoke out boldly, saying, “It was necessary that the word of God be spoken first to you. Since you thrust it aside and judge yourselves unworthy of eternal life, behold, we are turning to the Gentiles.
Further, when we read Revelation 4 and 5 we see the church in heaven with Christ and all angels worshiping God.
The 24 Elders represent the church which is indicated by the fact that they have white robes and crowns. The number 24 represents the entire priesthood (1 Chronicles 24:1-4, 19) . Since they are sitting on the throne, a place promised for the church alone (Revelation 3:21; Matthew 19:28). The white robes suggest they represent the church since in Isaiah 61:10 it represents righteousness imputed to the believer. It was promised to those in Sardis Rev. 3:4-5. The crowns since the crowns being worn are not monarchs crowns but victors crowns which are then thrown at Christ's feet in Rev 4:10.
This is not an exhaustive explanation but it is a start.
