It was on a Wednesday, three days before the Jewish Passover.  Seated around the table were the Lord Jesus Christ and the ones whom He had chosen to become the foundations of His Holy City.  The incarnate Logos was partaking of the last supper that He was ever going to have, with those who were to change the History of the world. (John, 13:1,2, etc.) 

The parting moments were deeply moving.   Jesus Christ would soon be dying on a wooden cross, and would be reunited with the one who had said:

3 “For I baptize you with water unto repentance, but the One who comes after me is mightier than I, whose sandals I am not worthy of carrying.  He will baptize you with the Holy Spirit and fire.”    [Matthew 3:11]

After him (John the Baptist), the time had now come for the Lord Himself to speak about this baptism:

“ 7 But I am telling you the truth. It is to your advantage that I go away; for if I do not go away, the Helper will not come to you; but if I do go away, then shall I send Him to you. 8 And, having come to you, He (will be the One who) will check (monitor) the world for sin, and for righteousness, and for judgment: 9 For sin, because they (of the world) do not believe in Me; 10 For righteousness, because I am going to My Father and you (will) no longer see Me; 11 For judgment, because the ruler of this world has been judged.  12 “I have many more things to tell you, but you cannot bear them now. 13 However, when He, the Spirit of truth comes, He will guide you into the entire truth; for He will not speak on His own authority, but whatever He will hear, He will say; and He will announce to you the things that are to come. 14 He will glorify Me, for He will take of what is Mine and announce it to you. 15 Everything that the Father has, is Mine. It is for this reason, that I said: ‘He will take of what is Mine and announce it to you.”     [John 16:7-15]  

“ 49 And behold, I send the Promise of the Father to you;  you however (should) tarry in the city of Jerusalem, until you are endued with power from on high.”   [Luke 24: 49]

In the days that followed, the words of the Lord Jesus were fulfilled completely.  He was crucified; He rose from the dead on the third day; and for 40 days thereafter, He prepared His disciples for their mission.  Hence, He did not omit to remind them of the things He had told them during their last meal together, prior to His death:

“ 4 And while keeping company with them, He instructed them: Do not depart from Jerusalem, but wait for the Promise of the Father, which you heard about from Me; for (although) John baptized in water, you however shall be baptized in the Holy Spirit, not many days from now.”    [Acts 1:4,5]

“ 8 But you shall receive power, after the Holy Spirit has come upon you, and you shall be witnesses to Me, both in Jerusalem and all of Judea and Samaria, and to the ends of the earth.”    [Acts 1:8]

Indeed, His disciples did not depart from Jerusalem. They remained there, waiting for the “Promise of the Father”, for the “Baptism by the Holy Spirit”; for the “Other Paraclete (Comforter)”.