According to Jehovah's Witnesses and Unitarians and all who deny that Jesus is the Almighty God, how can He be in you and live in you? Colossians 1:26-27: &quot;the mystery which has been hidden from the past ages and generations; but has now been manifested to His saints. To who God willed to make known what is the riches of the glory of this mystery among the Gentiles, which is Christ in you, the hope of glory.&quot;

How can you fellowship with someone who is NOT with (or in) you, and how can he be with (or in) you if he is not God? Jeremiah 17:10, &quot;I, the Lord, search the heart, I test the mind. Even to give to each man according to his ways, According to the results of his deeds.
The Apostle John at Revelation 2:23 excerpts the words from Jeremiah 17:10 and attributes them to the Lord Jesus Christ when He says, &quot;I am He who searches the minds and hearts; and I will give each one of you according to your deeds.&quot;
John 14:23 says God the Father and Jesus Christ will make their ABODE with him.&quot; Romans 5:5 says of the Holy Spirit, &quot;and hope does not disappoint, because the love of God has been poured out WITHIN OUR HEARTS through the Holy Spirit who was given to us.&quot;
So in summary, if Jesus Christ is not God how is it He can fellowship with billions of other peoples scattered throughout time and space?
The New World Translation does away with any need for Jehovah’s Witnesses to answer the question you raise by employing the simple expedience of altering the words in these Bible verses:

Colossians 1:26-28 NWT: “the sacred secret that was hidden from the past system of things and from the past generations.  But now it has been made manifest to his holy ones, to whom God has been pleased to make known what are the glorious riches of this sacred secret in union with you, the hope of his glory.  He is the one we are publicizing, admonishing every man and teaching every man in all wisdom, that we may present every man complete in union with Christ.”

It is worth noting that the New World Translation has changed virtually every verse that says “in me” or “in us” or “in them” to say “in union with me” or “in union with us” or “in union with them” (John 14:10, 11, 20; John 17:21, 22, 23).
However, there is no basis for translating the Greek text to read &quot;in union with&quot;.  I refer you to this question and the two answers that relate to this: https://hermeneutics.stackexchange.com/questions/59807/what-is-the-basis-for-translating-colossians-127-28-to-in-union-with-christ-a
In other words, the New World Translation does not say that Jesus dwells IN the believer, only that the believer is IN UNION WITH Christ.  This is not physical but is a spiritual relationship.

Romans 5:5 NWT: “the love of God has been poured out into our hearts through the holy spirit, which was given us.”

Likewise, the holy spirit is not a “who” but is a “which”.  Jehovah’s Witnesses believe that the holy spirit is God’s power in action, his active force. That is why they never show holy spirit as Holy Spirit.
John 14:23 NWT: In answer Jesus said to him: “If anyone loves me, he will observe my word, and my Father will love him, and we shall come to him and make our abode with him.”  This is taken to mean that those who love and obey Jesus will enjoy a close spiritual relationship with Jehovah and with Jesus.  It is not a literal, physical abode within the believer.

Question: What precious relationships are open to the anointed and to the “other sheep”?
10 Later that night, in answer to a question put to him by the faithful apostle Judas (Thaddaeus), Jesus said: “If anyone loves me, he will observe my word, and my Father will love him, and we shall come to him and make our abode with him.” (John 14:22, 23) Even while still on earth, anointed Christians, called to reign with Christ in heaven, have a particularly close relationship with Jehovah and with his Son. (John 15:15; 16:27; 17:22; Hebrews 3:1; 1 John 3:2, 24) But their “other sheep” companions, whose hope is to live forever on earth, also have a precious relationship with their “one shepherd,” Jesus Christ, and with their God, Jehovah, provided they prove to be obedient.  Source: https://www.jw.org/en/library/magazines/w20020201/Are-You-Among-Those-Loved-by-God/

The New World Translation agrees that it is Jehovah speaking in Jeremiah 17:10 and it is the Son of God speaking in Revelation 2:23.  However, they do not understand this to mean that Jehovah and Jesus are one and the same being.  Jesus (a created being and so perceived as a little god) is subordinate to Jehovah (the only big God) according to John 1:1 in the New World Translation. Jehovah's Witnesses believe that Jesus imitates his Father and is given authority by his Father to act.

John 5:19-24 NWT: The Son cannot do a single thing of his own initiative, but only what he beholds the Father doing...  For the Father judges no one at all, but he has committed all the judging to the Son.”

According to Jehovah’s Witnesses, Jesus can only ever do anything THROUGH the Father who created him.