Zechariah 12:10 refers to the promised latter rain that will precede the final harvest. The Lord is waiting patiently until His last rain is outpoured because it will produce the final harvest!
In the early part of this century, a Pentecostal movement began in Canada called the "Latter Rain Movement." It lasted perhaps forty or fifty years. Today, only a few "Latter Rain" churches remain. Yet those who were involved in that movement were convinced they were experiencing the Spirit's great, final outpouring. Many said, "This is it!" But the movement dissipated. And other such movements have come and gone also. Why? Because they were not focused on the harvest!
Many so-called Holy Ghost movements vanished quickly because they were man-centered—focusing on gifts, blessings, self-improvement, happiness. Dancing, laughing, roaring, or any other manifestation attributed to the Holy Ghost is all flesh unless it produces a broken heart for the lost and unsaved. If it is truly of the Spirit, it will result in a hunger and inclination to reach a lost and dying world!
Jesus tied the harvest to lost souls when He said, "Pray ye therefore the Lord of the harvest, that he will send forth labourers into his harvest" (Matthew 9:38).
Any true outpouring of the Holy Spirit will focus on this prayer of Jesus. And the few revivals documented as genuine all were blessed with great harvests of souls. There is no true revival without a great ingathering of lost souls!
Consider what happened as a result of Joel 2:28. At Pentecost, 3,000 people were saved in one day and souls were added daily afterward. These believers then were thrust out into all the world to witness Christ to the lost.
"Until the spirit be poured upon us from on high, and the wilderness be a fruitful field, and the fruitful field be counted for a forest" (Isaiah 32:15). Isaiah is saying here, "When the Holy Ghost comes, He produces fruit for the harvest. Lost souls are won in abundance!"