The Christian Church was born on the Day of Pentecost at about 30 AD.
Up until this time, Jesus had proclaimed the Kingdom of God and was put to death some seven weeks prior.
The disciples of Jesus along with the women including Mary the mother of Jesus were praying together for a number of days.
All of a sudden, they all "got excited" and started talking very loudly.
And a very strange thing happened.
They started speaking in languages they did not know.
There was such a commotion, it attracted a crowd.
Some said the disciples were drunk.
Others were astonished in hearing their native language come from those who did not even understand that language.
One of the disciples, the Apostle Peter, began to speak:

"Ye men of Judaea, and all ye that dwell at Jerusalem, be this known unto you, and hearken to my words: For these are not drunken, as ye suppose, seeing it is but the third hour of the day.
But this is that which was spoken by the prophet Joel;

"And it shall come to pass in the last days, saith God, I will pour out of my Spirit upon all flesh: and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams: And on my servants and on my handmaidens I will pour out in those days of my Spirit; and they shall prophesy And I will shew wonders in heaven above, and signs in the earth beneath; blood, and fire, and vapour of smoke The sun shall be turned into darkness, and the moon into blood, before the great and notable day of the Lord come And it shall come to pass, that whosoever shall call on the name of the Lord shall be saved.
"

"Ye men of Israel, hear these words; Jesus of Nazareth, a man approved of God among you by miracles and wonders and signs, which God did by him in the midst of you, as ye yourselves also know Him, being delivered by the determinate counsel and foreknowledge of God, ye have taken, and by wicked hands have crucified and slain: Whom God hath raised up, having loosed the pains of death: because it was not possible that he should be holden of it.
For David speaketh concerning him,

"I foresaw the Lord always before my face, for he is on my right hand, that I should not be moved: Therefore did my heart rejoice, and my tongue was glad; moreover also my flesh shall rest in hope Because thou wilt not leave my soul in hell, neither wilt thou suffer thine Holy One to see corruption.
Thou hast made known to me the ways of life; thou shalt make me full of joy with thy countenance.
"

"Men and brethren, let me freely speak unto you of the patriarch David, that he is both dead and buried, and his sepulchre is with us unto this day Therefore being a prophet, and knowing that God had sworn with an oath to him, that of the fruit of his loins, according to the flesh, he would raise up Christ to sit on his throne He seeing this before spake of the resurrection of Christ, that his soul was not left in hell, neither his flesh did see corruption.
This Jesus hath God raised up, whereof we all are witnesses Therefore being by the right hand of God exalted, and having received of the Father the promise of the Holy Ghost, he hath shed forth this, which ye now see and hear.
For David is not ascended into the heavens: but he saith himself,

"The Lord said unto my Lord, Sit thou on my right hand, Until I make thy foes thy footstool.
"

"Therefore let all the house of Israel know assuredly, that God hath made the same Jesus, whom ye have crucified, both Lord and Christ.
"[Acts 2:14b-36]

This message had an astounding effect.
The hearers wanted to know what to do next.
Again Peter speaks:

"Repent, and be baptized 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.
For the promise is unto you, and to your children, and to all that are afar off, even as many as the LORD our God shall call.
"[Acts 2:38b- 39]

That one sermon to that one group who were "in the public square", resulted to 3,000 converts to Christianity.
And they were all baptized.
And they continued in the faith as instructed by the Apostles.
That was also the start of the Roman Catholic Church.
Verse 10 explicitly mentions, in addition to Jews and citizens from other countries, "and strangers of Rome".
That is certainly understandable as the country was under Roman occupation.
The church in Rome grew so much that the Apostle Paul devoted the entire epistle to the Romans even before he went there.
History confirms that the Roman Church existed underground (actually literally) right through the worse persecution.
It continues to this day.
But the best part is the last statement of Peter cited above: "For the promise is unto you, and to your children, and to all that are afar off, even as many as the LORD our God shall call.
"That brings this old sermon 2,000 years forward to today.
We are from 30 AD, certainly "far off".
I suggest you use that sermon.
I quote it here in the old King James version where there is no copyright.
Choose a modern translation, if you desire.
God's Word will not return void.