For where two or three are gathered in my name, there am I among them. -- Matthew 18:20 (ESV)

and

Behold, I am with you always, to the end of the age. -- Matthew 28:20 (ESV)

It is physically impossible for a human to be omnipresent. If Jesus really meant that he would always be present with billions of Christians all over the world, it would mean that Jesus has to be divine.

However, this argument ignores the scriptures that state that Jesus could not be present everywhere and that he was leaving his disciples behind and will be returning (John 17). However, Trinitarians would argue that Jesus meant that his human body which cannot be omnipresent would leaven and return, but that he would also be "spiritually present" as like the Holy Spirit.

Jesus meant to be spiritually present

Being "spiritually present" is a vague statement. Even Paul said that:

When you are assembled in the name of the Lord Jesus and my spirit is present, with the power of our Lord Jesus, you are to deliver this man to Satan for the destruction of the flesh, so that his spirit may be saved in the day of the Lord. -- 1 Corinthians 5:4-5 (ESV)

Surely Paul is not divine and neither was he omnipresent.

Therefore, some suggest that like Paul, Jesus words should not be considered literally as if he would be physically "among" or "with" all Christians always.

So what was the intent for Jesus and Paul's statements?

• This could perhaps mean that both Jesus and Paul meant that when the assembly are in agreement to God's Holy Spirit, then they are acting in the same spirit of the Lord Jesus and of Paul as if Jesus or Paul was present or among them such that they are united as "one".
• It could also perhaps mean that both Jesus and Paul passed on their authority (approval) to their disciples so that they were able to make decisions as if Jesus or Paul was present to give approval.

Jesus meant it literally

Some reject the argument that Jesus words should be considered "spiritually" as there are no evidence that he was speaking in idioms, neither did he mention anything about the spiritual realm.

Matthew 18:20

The word translated as "among" is actually could also mean "middle" or "between".

Again I say to you, if two of you agree on earth about anything they ask, it will be done for them by my Father in heaven. For where two or three are gathered in my name, there am I between them. -- Matthew 18:19-20 (ESV)

Jesus could have meant that he is between the Father in heaven and those who gathered in his name as a mediator.

Matthew 28:20

Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age. -- Matthew 28:19-20 (ESV)

In this context Jesus was concerned about the eternal salvation of people. The purpose of making "disciples of all nations" was to make it possible for them to live forever in the presence of Jesus. Jesus previously said that he would return to gather his own (Matthew 24:23-44). Although he is currently not physically present yet, he will be in the future and this is something to look forward to (Matthew 19:28-30).

Furthermore, a parallel witness in the book of Acts states:

So when they had come together, they asked him (Jesus), “Lord, will you at this time restore the kingdom to Israel?”
He said to them, “It is not for you to know times or seasons that the Father has fixed by His own authority. But you will receive power when the Holy Spirit has come upon you, and you will be my witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth.”

And when he had said these things, as they were looking on, he was lifted up, and a cloud took him out of their sight. And while they were gazing into heaven as he went, behold, two men stood by them in white robes, and said,

“Men of Galilee, why do you stand looking into heaven?
This Jesus, who was taken up from you into heaven, will come in the same way as you saw him go into heaven.”

-- Acts 1:6-11 (ESV)

In this passage, Jesus referred to his Father as a distinct person with more authority.

What is also surprising is that none of the disciples ever questioned Jesus or asked him or the angels why he contradicted himself when he said that he will "always be present with them", yet after saying those words, he left them. Instead of questioning Jesus omnipresence they "looked into heaven". This hint that the disciples did not understand Jesus statement as an omnipresence claim.

It is also confirmed when the "two men in white robes" confirms that Jesus really left them. If Jesus was truly omnipresent from that moment, he would have appeared to them himself, and it would not have been necessary for God to send two men.