Then His people remembered the days of old, of Moses. Where is He who brought them up out of the sea with the shepherds of His flock? Where is He who put His Holy Spirit in the midst of them, who caused His glorious arm to go at the right hand of Moses, who divided the waters before them to make for Himself an everlasting name? ...Oh, that You would rend the heavens and come down, that the mountains might quake at Your presence! (please read fully Isaiah 63: 7-15)
If you can remember a time when God was much more active in your life than He is right now, recognize the ways in which you have been grieving Him. Ask His forgiveness and beg Him to make Himself real to you again!
God had been reaching out to Israel with love and blessing, but Israel chose to ignore God and go their own way. They grieved His Holy Spirit. So God stopped His obvious activity in their lives. After a long time, Israel started to remember the days when God was so active among them. "Why isn't God working like that any more?" they asked. They became desperate for Him.
Do you miss the way God used to be involved in your life, the way He used to reveal Himself to you and answer your prayers? God is waiting for you to be desperate enough to return to Him.