When did the Church begin?

It is unfortunate that when Christians speak about when the church started that it divides God's people and puts them into different theological camps based on their understanding of the Bible.

The one true church is the assembling of EVERYONE to worship our Father.

Most Christians today believe and teach that the Church started on the day of Pentecost. When Jesus tells Peter, "I will build my church...." was a forecast of what was to come upon His death and resurrection. Jesus asked His disciples in Matthew 16:13, "whom do men say that I the son of man am?" Peter answers, "Thou art the Christ, the son of the living God." Jesus goes on to tell Peter that, "upon this rock" or Peter's faith, He will make this the foundation of His church. Matthew 16, is where "church" is first mentioned. Since Jesus is the one who stated this, then it would hold some merit. Many argue today that the "assembly" of the people of God is one, therefore is a mistake to teach that the church began at Pentecost. Church leaders refer to the Old Testament people who gather and worship God as the "church". But this is Israel, God's chosen people, and the gentile nations had not yet been indoctrinated into God's church yet. When Jesus says that He will build His church, He is referring to everyone, including gentiles.

Church
The Greek word for church is Ekklesia. This comes from two words that mean, "called" and "out from and to." So, two Christians stepping out and assembling themselves out from the world to worship God, can be the church. The Bible describes the church as "the body of Christ" and uses marriage as Christ's relationship with the church. Most Christians believe the church started the day of Pentecost in Acts chapter 2 when over a hundred followers of Christ received the Holy Spirit and later that day after hearing Peter preach the word, thousands were saved.

Ephesians 1:22-23 "And hath put all things under his feet, and gave him to be the head over all things to the church, which is his body, the fullness of him that filleth all in all." The church could have NO functioning head until AFTER the death and resurrection of Jesus.

Ephesians 4:11-13 "And he gave some, Apostles; and some Prophets; and some Evangelists; and some Pastors and Teachers; for the perfecting of the saints, for the work of the ministry, for the edifying of the body of Christ: Till we all come in the unity of the faith." When Jesus is talking to Peter about the church, the aim of His ministry is in this verse, "for the edifying of the body of Christ."

It is unfortunate that when Christians speak about when the church started that it divides God's people and puts them into different theological camps based on their understanding of the Bible. 1 Corinthians 12:12-14 speaks of believers being "one body" and that it doesn't matter if you are "Jew or Gentile". We as believers in Christ are one body or one church.

Acts 1:4-5 "being assembled together.......but wait for the promise of the Father......but ye shall be baptized with the Holy Ghost not many days hence." Many point to this passage as showing that the church had not started until the receiving of the Holy Spirit. Acts 7:38 "This is he, that was in the church..." Stephen is speaking to the Israelites who have accused him of disrespecting Moses and the law. "church" is used to describe the gathering of these Israelites and is not to be misunderstood as the church we know of today. The Greek term "Ekklesia", sometimes possesses its general sense of congregation or assembly. In this passage, it is used for the gathering of the nation of Israel when it received the law.

The first time Jesus meets Peter is in John 1:35-43. It is also the first for Andrew too. Andrew finds his brother Peter and takes him to meet Jesus. It is at this encounter that our Savior calls Peter, "Cephas", which means stable as a rock(Aramaic). In Greek, Peter means "rock". The next time Peter meets Jesus is when Jesus starts His ministry, in Matthew 4:18-20. Jesus says, "follow me. I will make you fishers of men." Andrew and Peter were casting their nets, but immediately dropped what they were doing to start this journey with Jesus. Although Jesus had already met with some of His disciples, this doesn't mean He had started the church. It is only the BEGINNING of His teachings and guidance of introducing to them the start of the church.

Assembling of church in the Old Testament
In Deuteronomy 4:10, "Gather me the people together and I will make them hear my words, that they may learn to fear me all the days that they shall live upon the earth, and that they may teach their children." This "gathering" of people is that of Israel as an act of obedience to God's law. The one true church is the assembling of EVERYONE to worship our Father.

I think that the letter to the Romans particularly chapter 9 is clear. The dispensationalist concept is wrong. There is and always has only ever been one people of God. They are those who are so by Grace and faith.
Even in the "old testament" it is made clear by the numbers of non-Israelites who are saved by faith and by the numbers of Israelite who die by their faithlessness.
And Gentiles are grafted into Abraham while some of his descendents by flesh are cut off.

I think that the letter to the Romans particularly chapter 9 is clear. The dispensationalist concept is wrong. There is and always has only ever been one people of God. They are those who are so by Grace and faith.
Even in the "old testament" it is made clear by the numbers of non-Israelites who are saved by faith and by the numbers of Israelite who die by their faithlessness.
And Gentiles are grafted into Abraham while some of his descendents by flesh are cut off.

My own opinion is that the new testament Church came into being when the very first person believed in Jesus as Lord and put their faith in Him...

Many believe that very first person is Abraham.

Abraham is thee first to receive the Gospel. There is but one Gospel.

Question: If we are the same, where did those OT saints go when they died? Where they absent from the body and present with the Lord?

Romans 10:5–8 (LEB): 5 For Moses writes about the righteousness that is from the law: “The person who does this will live by it.”  6 But the righteousness from faith speaks like this: “Do not say in your heart, ‘Who will ascend into heaven?’ ” (that is, to bring Christ down), 7 or “Who will descend into the abyss?” (that is, to bring Christ up from the dead). 8 But what does it say? “The word is near to you, in your mouth and in your heart” (that is, the word of faith that we proclaim)

Continue reading in Romans

When did the Church begin? .

Most Christians today believe and teach that the Church started on the day of Pentecost. When Jesus tells Peter, "I will build my church...." was a forecast of what was to come upon His death and resurrection. Jesus asked His disciples in Matthew 16:13, "whom do men say that I the son of man am?" Peter answers, "Thou art the Christ, the son of the living God." Jesus goes on to tell Peter that, "upon this rock" or Peter's faith, He will make this the foundation of His church. Matthew 16, is where "church" is first mentioned. Since Jesus is the one who stated this, then it would hold some merit. Many argue today that the "assembly" of the people of God is one, therefore is a mistake to teach that the church began at Pentecost. Church leaders refer to the Old Testament people who gather and worship God as the "church". But this is Israel, God's chosen people, and the gentile nations had not yet been indoctrinated into God's church yet. When Jesus says that He will build His church, He is referring to everyone, including gentiles.

Church
The Greek word for church is Ekklesia. This comes from two words that mean, "called" and "out from and to." So, two Christians stepping out and assembling themselves out from the world to worship God, can be the church. The Bible describes the church as "the body of Christ" and uses marriage as Christ's relationship with the church. Most Christians believe the church started the day of Pentecost in Acts chapter 2 when over a hundred followers of Christ received the Holy Spirit and later that day after hearing Peter preach the word, thousands were saved.

Ephesians 1:22-23 "And hath put all things under his feet, and gave him to be the head over all things to the church, which is his body, the fullness of him that filleth all in all." The church could have NO functioning head until AFTER the death and resurrection of Jesus.

Ephesians 4:11-13 "And he gave some, Apostles; and some Prophets; and some Evangelists; and some Pastors and Teachers; for the perfecting of the saints, for the work of the ministry, for the edifying of the body of Christ: Till we all come in the unity of the faith." When Jesus is talking to Peter about the church, the aim of His ministry is in this verse, "for the edifying of the body of Christ."

It is unfortunate that when Christians speak about when the church started that it divides God's people and puts them into different theological camps based on their understanding of the Bible. 1 Corinthians 12:12-14 speaks of believers being "one body" and that it doesn't matter if you are "Jew or Gentile". We as believers in Christ are one body or one church.

Acts 1:4-5 "being assembled together.......but wait for the promise of the Father......but ye shall be baptized with the Holy Ghost not many days hence." Many point to this passage as showing that the church had not started until the receiving of the Holy Spirit. Acts 7:38 "This is he, that was in the church..." Stephen is speaking to the Israelites who have accused him of disrespecting Moses and the law. "church" is used to describe the gathering of these Israelites and is not to be misunderstood as the church we know of today. The Greek term "Ekklesia", sometimes possesses its general sense of congregation or assembly. In this passage, it is used for the gathering of the nation of Israel when it received the law.

The first time Jesus meets Peter is in John 1:35-43. It is also the first for Andrew too. Andrew finds his brother Peter and takes him to meet Jesus. It is at this encounter that our Savior calls Peter, "Cephas", which means stable as a rock(Aramaic). In Greek, Peter means "rock". The next time Peter meets Jesus is when Jesus starts His ministry, in Matthew 4:18-20. Jesus says, "follow me. I will make you fishers of men." Andrew and Peter were casting their nets, but immediately dropped what they were doing to start this journey with Jesus. Although Jesus had already met with some of His disciples, this doesn't mean He had started the church. It is only the BEGINNING of His teachings and guidance of introducing to them the start of the church.

Assembling of church in the Old Testament
In Deuteronomy 4:10, "Gather me the people together and I will make them hear my words, that they may learn to fear me all the days that they shall live upon the earth, and that they may teach their children." This "gathering" of people is that of Israel as an act of obedience to God's law. The one true church is the assembling of EVERYONE to worship our Father.

If by "gospel" you mean good news, I agree completely. If by "gospel" you mean "church", I would say those are two different words and have different meanings.