The latter rain occurs when, prior to Christ's second coming, the Holy Spirit is given to the church in special measure. Full consecration to Jesus prepares us for that experience. Reference: E.G. White, "The Upward Look," p. 283.

Full text of the devotional: “Preparation for the Latter Rain,” September 26

Ask ye of the Lord rain in the time of the latter rain; so the Lord shall make bright clouds, and give them showers of rain, to every one grass in the field. Zechariah 10:1.

If you will be faithful to God, self shall be crucified; self shall die, and Christ Jesus shall live in us, and He shall be the hope of our calling; we will represent Jesus Christ to the world. Inquire sincerely, “Am I a Christian?” If I am a Christian, I am looking unto Jesus, the Author and the Finisher of my faith. In Him my hopes of eternal life are centered...

We need not worry about the latter rain. All we have to do is to keep the vessel clean and right side up and prepared for the reception of the heavenly rain, and keep praying, “Let the latter rain come into my vessel. Let the light of the glorious angel which unites with the third angel shine upon me; give me a part in the work; let me sound the proclamation; let me be a colaborer with Jesus Christ.” Thus seeking God, let me tell you, He is fitting you up all the time, giving you His grace.

You need not be worried. You need not be thinking that there is a special time coming when you are to be crucified. The time to be crucified is just now. Every day, every hour, self is to die; self is to be crucified; and then, when the time comes that the test shall come to God’s people in earnest, the everlasting arms are around you. The angels of God make a wall of fire around about and deliver you.

All your self-crucifixion will not do any good then. It must be [done] before the destiny of souls is decided. It is now that self is to be crucified—when there is work to do; when there is some use to be made of every entrusted capability. It is now that we are to empty and thoroughly cleanse the vessel of its impurity. It is now that we are to be made holy unto God. This is our work, this very moment. You are not to wait for any special period for a wonderful work to be done; it is today. I give myself to God today...

Are you ready to make the surrender now? You are to put away your sin right now when you see it... Do not make leeway [that] you are going to overcome by degrees; you are going to try little by little to give up sin. Now, while it is called today, heed the invitation and harden not your hearts.

Oh, my soul, why not leave the cursed thing today? Sin crucified my Lord. Why not turn from it with loathing? Why not love the things that Christ loved, and hate the things that Christ hated? He has made provision ample enough for you that you can, through Him, be more, yea, more than overcomers.—Manuscript 35, September 26, 1891, “Work and Baptism of Holy Spirit Needed.”