A servant does not know what his master is doing

John 15:13-15
Greater love has no one than this, than to lay down one’s life for his friends. 14 You are My friends if you do whatever I command you. 15 No longer do I call you servants, for a servant does not know what his master is doing; but I have called you friends, for all things that I heard from My Father I have made known to you. 

This is one of the various passages that debunk the myth that God works in mysterious ways. All through history, from examples with Abraham, to Moses, David and Yshua, God has revealed His plans to people. Previously it was to the prophets, but after Christ, where we have the Holy Spirit in us, we too have been revealed His plans. So for any believers who still think God's plans are mysterious, it is time to walk closer with God and have more frequent communion with Him.