Acts 1:4 (CSB) While he was with them, he commanded them not to leave Jerusalem, but to wait for the Father's promise. "Which," he said, "you have heard me speak about;

Since the disciple faith got stronger when they went to Galilee, for their vacation / getaway in the first few day after Jesus resurrection (Matthew 28:16-20). Now they are being told to stay in Jerusalem, on these last few days before Jesus is finally taken to heaven until his second return, to be given Power from on High (Luke 24:49, Acts 2:1-4). They are to remain in Jerusalem just as the 70 was to gather in God's tent in the days of Moses (Numbers 11:24-30).  However those who would not stay in the room did not receive the spirit in the first giving of the spirit but may have after Peter's sermon.

Numbers 11:24-30 (CSB) 24 Moses went out and told the people the words of the LORD. He brought seventy men from the elders of the people and had them stand around the tent. 25 Then the LORD descended in the cloud and spoke to him. He took some of the Spirit that was on Moses and placed the Spirit on the seventy elders. As the Spirit rested on them, they prophesied, but they never did it again. 26 Two men had remained in the camp, one named Eldad and the other Medad; the Spirit rested on them -- they were among those listed, but had not gone out to the tent -- and they prophesied in the camp. 27 A young man ran and reported to Moses, "Eldad and Medad are prophesying in the camp." 28 Joshua son of Nun, assistant to Moses since his youth, responded, "Moses, my lord, stop them! " 29 But Moses asked him, "Are you jealous on my account? If only all the LORD's people were prophets and the LORD would place his Spirit on them! " 30 Then Moses returned to the camp along with the elders of Israel.