The phrase "when the day of Pentecost was fully come" in Acts 2:1 does not support the observance of Pentecost on a Monday. The word "Pentecost" means the 50th day, not the 51st. The Greek word translated as "fully" in this verse is sumpleerousthai, an infinitive form of sumpleero, meaning to fulfill or fill full. This word, combined with the preposition en and the definite article, forms a present tense articular infinitive, indicating that the action of fulfilling was ongoing at the time. Therefore, the phrase should be understood as "during the accomplishing of the day, the 50th day," which was a Sunday. This interpretation aligns with translations such as "While the Day of Pentecost was running its course" and "During the course of the Day of Pentecost," confirming that the 50th day was being accomplished on a Sunday, not completed on a Monday.

Pentecost is the only holy day during the year that God commands to be counted. This sets everything up for understanding through counting. The other appointed times are set dates on the Hebrew calendar. Pentecost does not work that way. God says to count it from the day after the Sabbath. This requires counting seven weeks of Sabbaths down to the fiftieth day. From this basic beginning idea of counting parts of time the day of Pentecost has a lot to do with time. Time is one of Pentecost's themes because God wants awareness of this counting process of time. Even Acts 2:1 alludes to this principle when it says now when the day of Pentecost had fully come. That phrase literally means and when the day of Pentecost was being fulfilled. It has a dual meaning. The physical meaning is that the fifty days had been fully counted and the actual day of Pentecost had been reached. The counting of the day of Pentecost had been fulfilled. It can also mean that the symbolism of the day of Pentecost was being fulfilled. It has both a physical and a spiritual meaning. The word Pentecost means count fifty. This focus on time leads to the conclusion that the fifty days of the count to Pentecost using the day-for-a-year principle represent the years of a converted person's life generally fifty years. That is a normal person's span of time. God gives most of a lifetime to live with Him in this life to overcome and grow and to put on the righteous character of our Lord and Savior Jesus Christ. That is what Pentecost focuses on those converted years of our lives when people are being made into that wavesheaf offering as it were when they are being made acceptable before God. The time of conversion those fifty years or whatever they happen to be is the window to sync up with God.

On the Day of Pentecost the term had fully come is more accurately translated from the Greek as was being fulfilled. When the Day of Pentecost was being fulfilled the disciples were all with one accord in one place. The Spirit of God descended upon them in abundance and power. The gift of the Spirit was accompanied by supernatural and extraordinary manifestations. The disciples heard a sound from heaven which rushed with mighty force through the house and filled it as a storm rushes. There was no wind. It was the sound that filled the house not the wind and it was an inevitable cause producing audible effects. On the Day of Pentecost the Holy Spirit came and entered into those first 120 people in the church. It was the first time that there was any spiritual group salvation and it was the day that the church of God was established. Then 3,000 more were added. These were the ones that God had called. He had predestined them to be called at that time. The Day of Pentecost was when the church began with the power of the Holy Spirit being given to it. The Holy Spirit was given to empower the people to keep the Ten Commandments of God. It was given at the Temple so there is a consistency of the place where God chose to place His name and it was at the Temple. The gospel was enabled to be preached to the entire world and then God caused the miracle of the speaking of the apostles so that when they spoke in their own language it came out in the language of wherever they were from and those that came there to keep the Feast of Pentecost. This was also a prophecy that now people would be able to have access to God the Father through the Spirit into the temple in heaven. This was also a prophecy of the coming demise of the whole sacrificial Temple system.

When the Day of Pentecost had fully come, they were all with one accord in one place. Had fully come is more accurately translated from the Greek as was being fulfilled. The Day of Pentecost was when the church began with the power of the Holy Spirit being given to it. On the Day of Pentecost the Holy Spirit came and entered the first 120 of the church. It was the first time there was any group salvation. Three thousand more were added, and these were those God had called and predestined to be called at that time. God gave the Holy Spirit on the Day of Pentecost to empower the people to keep the Ten Commandments of God. The gift of the Spirit was accompanied by supernatural manifestations. The disciples heard a sound from heaven which rushed with mighty force into the house and filled it. The sound filled the house, not the wind. Tongues appeared as flames that rested on each of the apostles. They were all filled with the Holy Spirit and began to speak with other tongues as the Spirit gave them utterance. The apostles began to speak in other languages as the Spirit gave them words to proclaim. They preached the crucifixion and resurrection of Jesus Christ and the receiving of the Holy Spirit through repentance and baptism.