Most people could answer this question without hesitation: What is the most important birth in the entire Bible? Christmas makes that one easy. But here’s the harder question: What is the second most important birth in Scripture? In Genesis 21, a 90-year-old woman named Sarah finally gives birth to a son named Isaac, the child God had promised 25 years earlier. It sounds like a personal miracle for one elderly couple, but it was far more than that. That one birth set off a chain reaction, from Isaac to Jacob, from Jacob to Judah, from Judah to David, and from David to Jesus. Without Isaac, there is no Israel. Without Israel, there is no Jesus. Without Jesus, there is no Gospel. God is a missionary God, the Bible is a missionary book, and, if you have a heart for God, you will have a missionary heart.

What does it look like to be completely, unreservedly committed to God? In 1519, Spanish explorer Hernán Cortés sailed to Mexico with 11 ships, more than 500 men, and odds completely against him. When he arrived, he gave his men a shocking order: Burn the ships. Retreat was no longer an option. They were all in. Over 3,000 years earlier, a man named Abraham faced his own burn-the-ships moment. God had finally given him the son he had waited 25 years for, a boy named Isaac, and now God was asking Abraham to give him back. What happens on that mountain in Genesis 22 is one of the most breathtaking stories in all of Scripture. It shows us what giving really is, what giving really does, and why giving is one of the most important things you will ever do.

In algebra, x represents the unknown—the variable that, once you solve for it, makes everything else make sense. Abraham’s life looks that way too: unlikely candidate, impossible promise, uncertain path. But Genesis 15 reveals the x—the one variable that explains everything. It was faith in God. This chapter, which many scholars consider the most important in the entire Old Testament, reveals for the first time how a sinful human being can be made right with a holy God. Abraham shows us that faith isn’t passive; it drives out fear, it takes God at His word, and it holds on to His promises. There are three things Abraham did that activated the God factor in his life, and they’ll do the same in yours.