The cross was the core of the ministry of the angels and the Apostles
An important point is that the angel who proclaimed the Lord's resurrection said to the women: “...you seek Jesuswho was crucified. He is not here; for He is risen, as He said” (Matt.28: 5,6). Thus the angel called the Lord “who was crucified”, although He had already resurrected. Thus the title ‘crucified’ continued to be attributed to the Lord.
Our fathers the Apostles emphasised the Lord's crucifixion in their preaching. In preaching to the Jews, St. Peter said: “Therefore let all the house of Israel know assuredly that God has made this Jesus, whom you crucified, both Lord and Christ” (Acts2: 36). St. Paul says: “..we preach Christ crucified” (1Cor.1: 23), although the Lord's crucifixion was considered “a stumbling block and to the Greeks foolishness”.
The Apostle considered the cross the essence of Christianity and says: “For I determined not to know anything among you except Jesus Christ and Him crucified” (1Cor.2: 2). He means that the cross is the only subject he wants to know.