Acts 1:2

Until the day in which

(αχρ ης ημερας). Incorporation of the antecedent into the relative clause and the change of case η (locative) to ης (genitive).Was received up

(ανελημπθη). First aorist passive indicative of αναλαμβανω. Common verb to lift anything up (Acts 10:16) or person as Paul (Acts 20:13). Several times of the Ascension of Jesus to heaven (Mark 16:19; Acts 1:2; Acts 1:11; Acts 1:22; 1 Timothy 3:16) with or without "into heaven" (εις τον ουρανον). This same verb is used of Elijah's translation to heaven in the LXX (2 Kings 2:11). The same idea, though not this word, is in Luke 24:51. See Luke 9:51 for αναλημψις of the Ascension.Had given commandment

(εντειλαμενος). First aorist middle participle of εντελλω (from εν and τελλω, to accomplish), usually in the middle, old verb, to enjoin. This special commandment refers directly to what we call the commission given the apostles before Christ ascended on high (John 20:21-23; Matthew 28:16-20; Mark 16:15-18; 1 Corinthians 15:6; Luke 24:44-49). He had given commands to them when they were first chosen and when they were sent out on the tour of Galilee, but the immediate reference is as above.Through the Holy Spirit

(δια πνευματος αγιου). In his human life Jesus was under the guidance of the Holy Spirit. This applies to the choice of the apostles (Luke 6:13) and to these special commands before the Ascension.Whom he had chosen

(ους εξελεξατο). Aorist middle indicative, not past perfect. The same verb (εκλεξαμενος) was used by Luke in describing the choice of the twelve by Jesus (Luke 6:13). But the aorist does not stand "for" our English pluperfect as Hackett says. That is explaining Greek by English. The Western text here adds: "And ordered to proclaim the gospel."