God keeps His promises. Pentecost.

 God promised to King David,

"And when thy days be fulfilled, and thou shalt sleep with thy fathers, I will set up thy seed after thee, which shall proceed out of thy bowels, and I will establish his kingdom. He shall build an house [temple] for my name, and I will stablish the throne of his kingdom for ever.”- 2 Samuel 7:12-13 KJV

Jesus was born the son of David, preached the gospel of His kingdom, was crucified, buried, and on the third day rose from the dead. (John 3:5, John 2:19-21, Hebrews 3:3-6). Forty days later, He ascended into heaven. On the Day of Pentecost, Jesus poured out His Spirit on all those praying and waiting in the upper room. (Acts 1:4-5, Acts 2:4).

Peter then preached to the people that God had just poured out His promised Spirit. (Joel 2:28-29). Peter preached the gospel, then preached what David had spake concerning Jesus. Peter testified that God had kept His promise to David: those in the upper room were witnesses of Christ’s resurrection, and now all the people gathered were witnesses of God’s promised outpouring of His Spirit.

"Therefore being a prophet, and knowing that God had sworn with an oath to him, that of the fruit of his loins, according to the flesh, he would raise up Christ to sit on his throne; he seeing this before spake of the resurrection of Christ, that his soul was not left in hell [among the dead], neither his flesh did see corruption [rot in the grave].

“This Jesus hath God raised up, whereof we all are witnesses. Therefore being by the right hand of God exalted, and having received of the Father the promise of the Holy Ghost, he hath shed forth this, which ye now see and hear." - Acts 2:30-33 KJV

God keeps His promises.