Why did the disciples cast lots when the Holy Spirit was promised

In the book of Acts Chapter 1:v 4-5 regarding an earlier speech of Jesus, it is written >On one occasion,while he was eating with them he gave them this command:Do not leave Jerusalem,but wait for the gift my father promised,which you have heard me speak about. 5:For John baptised with water but in a few days you will be baptised with the Holy spirit. ---------- When the disciples were choosing one of their own to replace Judas,it is written Acts 1:v23-26 >So they proposed two men:Joseph called Barsabass (also known as Justus) and Matthias. 24:Then they prayed,"Lord,you know everyone's heart.Show us which of these two men you have chosen 25: to take over this apostolic ministry,which Judas left to go where he belongs." 26:Then they cast lots, and the lot fell to Matthias;so he was added to the eleven apostles. ---------- If they were to baptised by the Holy Spirit in a few days time,then why did they use a form of divination by casting lots to discover who to choose?