I think the OP has partially answered his own question. Let us remind ourselves that the Holy Spirit did not suddenly arrive for the first time at Pentecost in Acts 2 - the Holy Spirit had been active ever since the creation of the world in Gen 1 - see the appendix below.
Therefore, what did Jesus mean when He said, "the Holy Spirit would not come unless I go away" (Acts 16:7)?? Clearly, the Holy Spirit had been "filling" people for centuries!
I believe that Jesus' remark can be understood as a matter of fact rather than a condition. While Jesus was with the disciples physically (they could see and touch Him, 1 John 1:1), they would never need to exercise any faith about the invisible Holy Spirit. However, Jesus promised that the disciples would not be left alone - they would have another comforter, the Holy Spirit whom they would see only by the eye of faith based on the evidence of His presence.
Now, the fact that Jesus was physically absent most of the time, did not prevent His re-appearing to various people at various times such as:
- to Paul on the road to Damascus, Acts 9:1-15, see also 1 Cor 15:8
- to Paul on the storm tossed ship in Acts 27:23
- to Paul at his defense before Nero, 2 Tim 4:17
- to John in Rev 1-3
Note the comments of Albert Barnes on Matt 18:20 -
He affirms that wherever two or three are assembled together in his
name, he is in the midst of them. In my name - That is,
By my authority, acting for me in my church. See John 10:25; John 16:23.
It may mean for my service; in the place of prayer and praise, assembled in obedience to my commend, and with a desire to promote my
There am I in the midst of them - Nothing could more clearly prove
that Jesus must be omnipresent, and, of course, be God. Every day,
perhaps every hour, two or three, or many more, may be assembled in
every city or village in the United States, in England, in Greenland,
in Africa, in Ceylon, in the Sandwich Islands, in Russia, and in Judea
in almost every part of the world - and in the midst of them all is Jesus the Saviour. Millions thus at the same time, in every quarter of
the globe, worship in his name, and experience the truth of the
promise that he is present with them. It is impossible that he should
be in all these places and not be God.
Thus, according to Albert Barnes, Jesus is (after His resurrection) omnipresent. However, some might dispute this and say that Jesus is present only by the omnipresent work of the the Holy Spirit (John 14:16, 26, 15:26).
This is a vexed subject about which there is much valid debate. The simplest, most literal understanding is to take both positions literally and conclude that:
- Jesus is present will all of us via His Holy Spirit as promised in John 14:16, 26, 15:26
- Jesus is present personally where "two or three are gathered" (Matt 18:20).
However, I am not dogmatic about this.
APPENDIX - Holy Spirit before Pentecost
In the OT the Holy Spirit is described many times in the following ways:
- Involved in creation, Gen 1;2 (compare Deut 32:10, 11), Ps 104:30
- Empowering leaders such as Saul, 1 Sam 10:10, 19:21-24; Joseph, Gen 41:38; Othniel, Judg 3:10; Gideon, Judg 6:27-30, 34:7; Jephthah, Judg 11:29-32; Samson, Judg 13:24, 14:6, 19, 15:14; 70 leaders, Num 11:17, 26, 29; Joshua, Num 27:18; Elisha, 2 Kings 2:9, 15, etc.
- Inspiring craftsmen like Bazaleel, Ex 31:3, 35:31
- Inspiring prophets like Ezekiel, Eze 11;24; Balaam, Num 24:2; Azariah, 2 Chron 15:1-7; Zechariah, 2 Chron 24:20; Elijah, 1 Kings 18:12, 2 Kings 2:16; etc.
- Involved in the everyday lives of ordinary people to make them Godly, Isa 63:10, 11, Ps 51:11, Gen 6:3, Neh 9:30, Zech 7:12, Ps 106:33, 41, Joel 2:28.
- The Spirit is given personal and divine attributes: “good” (Ps 143:11); “generous” (Ps 51:12); facilitating what might and power cannot (Zech 4:6); grieved by human rebellion (Isa 63;10); etc.
- Involved in final judgement: Isa 4:4, 32;15, 42:1, 44:3, 48:20, Prov 1:23, etc.
Even in the NT before Pentecost (Acts 2) the Holy Spirit was active in several places such as the
- The conception of Jesus in Mary, Matt 1:18, 20, Luke 1:35
- John the Baptist would be filled with the Holy Spirit, Luke 1:15
- Elizabeth filled with the Holy Spirit, Luke 1:41
- Zechariah filled with the Holy Spirit, Luke 1:67
- The prophet Simeon instructed by the Holy Spirit, Luke, 2:25-27