The apostles were healing “every one” that came to them (5:16), so the religious leaders in Israel were “filled with indignation” (5:17) or anger, while the apostles were “filled with the Holy Ghost” (2:4). We too can choose to be filled with the Spirit instead of being filled with anger (Eph. 5:18) by being filled with God’s Word (Col.1:9,10).
These leaders were so angry they jailed the apostles (v.18) for the second time (4:1-3). But the Lord showed what He thought of their incarceration when He sent “the angel of the Lord” to spring them out of jail (5:19,20). That exact phrase sometimes referred to a theophany, a pre-incarnate appearance of Christ (cf. Ex. 3:2,4,6). But here it appears to be just one of God’s regular angels, who were “ministering spirits, sent forth to minister for them who shall be heirs of salvation” like the apostles (Heb. 1:14).
But if God’s people are always supposed to obey the government, why would God undermine the authority of Israel’s government by breaking the apostles that they incarcerated out of jail? It was because those men were no longer the legitimate rulers in Israel. The Lord had warned them He would take the kingdom away from them (Mt. 21:43) and give it to the “little flock” of His followers (Lu. 12:32). That means the apostles were the new leaders of Israel, so the old rulers were wrong to incarcerate the new leaders, and the angel did nothing wrong breaking the new leaders out of jail.
This jailbreak was predicted (Ps. 69:33). As it says there, the Lord helped the poor at Pentecost when He had the disciples sell all they had and give the proceeds to the poor to be saved (Lu. 18:18,22), and showed He didn’t despise His prisoners when He released them. We see Pentecost predicted again in Psalm 146:3-9, where the Jews were told not to trust princes like Israel’s leaders, the hungry are mentioned as being fed again when those proceeds were shared, and prisoners were loosed, causing the way of those wicked rulers to be turned upside down. You see, the psalms will be the guidebook of the Tribulation that these apostles were heading into if God hadn’t interrupted prophecy.
The angel told the apostles to go speak “all” the words of eternal life (5:20) because the apostles might have been tempted to omit the words the Sadducees didn’t want to hear, those about the resurrection of Christ (cf. Mt.22:23).
The only other time a “senate” (Acts 5:21) is referred to is Pharaoh’s (Ps. 105:20-22). He saw Joseph’s miraculous interpretation of his dream and freed him from prison and put him over his senators. That may be why the senate is mentioned here. When Israel’s senate convened, the Jews might have thought of Pharaoh’s senate and realized that their ruler (the high priest) should do what Pharaoh did: recognize the miracles that the apostles were doing and free them from prison and put them over his senate. It wouldn’t be the first time God shamed the Jews with the Gentiles (cf. Luke 4:25-30).
The high priest sent soldiers to fetch the apostles out of prison (Acts 5:21), not knowing the twelve were already free and teaching in the temple. The soldiers reported that the jail keepers didn’t see them escape (5:22), so the angel must have pulled an Acts 12:5-10 here. Notice that the leaders didn’t doubt that another miracle had taken place (cf. Acts 4:16), they only doubted “whereunto it would grow.” They feared the people would think the Spirit whisked them out of jail like He used to whisk Elijah around (I Ki. 18:12). But what had happened was a miracle, it didn’t need to grow!
When the high priest said that the apostles had “filled Jerusalem” with their doctrine (Acts 5:27,28), that wasn’t true. Sure, 3,000 men got saved the first day and 5,000 men the next day, but even counting their families, that was only a fraction of the estimated 600,000 people living in Jerusalem at that time. If they had filled Jerusalem with their doctrine, they would have moved on to spread the gospel to the rest of the world as the Lord told them (Lu. 24:47; Acts 1:8).The high priest only said that to get people to overreact (cf. Jo. 12:19).
The high priest was also wrong when he said the apostles were trying to bring the Lord’s blood on them, even though they said they were willing to bear responsibility for it (Mt. 27:3,4). The apostles had reduced the charge against them from murder to manslaughter (Acts 3:17), so weren’t.