The book I mentioned is “The Harbinger”. You can find it here.
Then we continue in Exodus Chapter 23 and make it through to verse 23.
Below are the relevant verses:
Exodus 23 (NIV)
13“Be careful to do everything I have said to you. Do not invoke the names of other gods; do not let them be heard on your lips.
14“Three times a year you are to celebrate a festival to me.
15“Celebrate the Festival of Unleavened Bread; for seven days eat bread made without yeast, as I commanded you. Do this at the appointed time in the month of Aviv, for in that month you came out of Egypt.
“No one is to appear before me empty-handed.
16“Celebrate the Festival of Harvest with the firstfruits of the crops you sow in your field.
“Celebrate the Festival of Ingathering at the end of the year, when you gather in your crops from the field.
17“Three times a year all the men are to appear before the Sovereign Lord.
18“Do not offer the blood of a sacrifice to me along with anything containing yeast.
“The fat of my festival offerings must not be kept until morning.
19“Bring the best of the firstfruits of your soil to the house of the Lord your God.
“Do not cook a young goat in its mother’s milk.
20“See, I am sending an angel ahead of you to guard you along the way and to bring you to the place I have prepared. 21Pay attention to him and listen to what he says. Do not rebel against him; he will not forgive your rebellion, since my Name is in him. 22If you listen carefully to what he says and do all that I say, I will be an enemy to your enemies and will oppose those who oppose you. 23My angel will go ahead of you and bring you into the land of the Amorites, Hittites, Perizzites, Canaanites, Hivites and Jebusites, and I will wipe them out.