Both the Old and New Testament use the symbolism of water to represent the Holy Spirit.
The prophet Isaiah quotes the words of our Lord, “‘“I will pour water on him who is thirsty. . . . I will pour My Spirit on your descendants”’” (Isa. 44:3, NKJV). Isaiah uses a common Hebrew literary device called parallelism. The second phrase in the passage explains the first. The prophet Joel also discusses the symbolism of water. God promises to water Israel’s fields, then declares, “‘And it shall come to pass afterward that I will pour out My Spirit on all flesh’” (Joel 2:28, NKJV). Jesus uses the symbolism of water to represent the Holy Spirit (John 7:37-39).
In Bible times, sowing and plowing took place from the middle of October, shortly after the falling of the early rains. These early rains brought the seed to germination and nurtured its early growth. The latter rain came in the late spring to bring the ripening fruit to harvest. The barley harvest and other grain harvests were spring events, followed by the fruit harvest in the summer and fall.
God uses the symbolism of the early and latter rain in two ways. The early rain of the Spirit fell upon the disciples at Pentecost in order to launch the Christian mission. The latter rain will be poured out on God’s church at the end of time in order to complete His mission on earth. The term the “early rain” also refers to the daily work of God’s Spirit convicting, instructing, guiding, and empowering each believer. The “latter rain” is a term used to describe a special endowment of God’s Holy Spirit on Christ’s church just before the coming of Jesus.
“Under the figure of the early and the latter rain, that falls in Eastern lands at seedtime and harvest, the Hebrew prophets foretold the bestowal of spiritual grace in extraordinary measure upon God’s church. The outpouring of the Spirit in the days of the apostles was the beginning of the early, or former, rain, and glorious was the result. . . .
“But near the close of earth’s harvest, a special bestowal of spiritual grace is promised to prepare the church for the coming of the Son of man. This outpouring of the Spirit is likened to the falling of the latter rain; and it is for this added power that Christians are to send their petitions to the Lord of the harvest ‘in the time of the latter rain.’”-Ellen G. White, The Acts of the Apostles , pp. 54, 55.