What does Acts 1:4 mean?
Luke resolves to give orderly accounts (Luke 1:3), but that does not mean his record is strictly chronological. Modern historical works strive to explain events in the order they occurred; this was not as much a priority for ancient historians. The phrase "while staying with them" means what it sounds like, but some scholars translate it to mean they are sharing a meal. Combined with the opening of Acts 1:6, which says "so when they had come together," it's evident the events included in Acts 1:4–11 occur over several days; perhaps even the forty days of Acts 1:3.Because of the timing of Jesus' resurrection—the day after the Sabbath of the Feast of Unleavened Bread—and the fact that the Holy Spirit comes on Pentecost (Acts 2:1–4), we know that the disciples wait in Jerusalem about nine days between Jesus' ascension and the coming of the Holy Spirit.
The "promise" was given to the Jews in Joel 2:28–32 which Peter quotes as it is being fulfilled (Acts 2:17–21). The Holy Spirit will pour out and give people direct messages. Great signs will envelop the heavens and earth heralding Jesus' return. And everyone who calls on Jesus' name will be saved.
In the book of Acts, the Holy Spirit does come on Jesus-followers (Acts 2:2–4; 8:17; 10:44; 19:6), and many receive messages and visions from God (Acts 5:19–20; 7:56; 8:26; 9:3–6, 11–15; 10:3–6, 10–16; 16:9; 21:8–11). But the passage reflects the tendency of biblical prophecy to compress future-looking timeframes. The blood, fire, and smoke, the darkened sun and the moon turning to blood, and the return of Jesus are in our future (Joel 2:30–31). But we can be sure that whoever calls on Jesus' name will be saved, both now and for eternity (Joel 2:32).
The "promise," specifically, is the baptism of the Holy Spirit (Acts 1:5). In the disciples' lifetime, some of them first heard about the promise from John the Baptist (Matthew 3:11; Luke 3:16). Jesus reiterated God's promise of the Holy Spirit (Luke 11:13; John 14:16–17, 26; 15:26) but the Holy Spirit can't come until Jesus leaves (John 16:7–14). The baptism of the Holy Spirit is that moment in which the Holy Spirit establishes an intimate and permanent connection with the new believer's soul. The Holy Spirit provides assurance of salvation (Romans 8:16), guidance (John 16:13), and membership in the body of Christ—the church (1 Corinthians 12:12–13).