There is a human tendency to loose trust in God as time elapses. It is common for a person to hear the promises of God, be excited about them in the moment, and as time progresses, loose interest and faith in God's ability and willingness to deliver on those promises. Depending on the expectation one has for God, sometimes the time God takes to do a certain work will even cause some to waiver in their faith to become angry at God, and some will even go to the extent to tell themselves that God is not real. However, these types of responses reflect one's ignorance regarding who God is and how He works. Rather than grow in unbelief or get bitter, one needs to get educated on how God works and then seek to ensure one's expectations are in line with how the Bible describes God's work habits.
For example, in Genesis 16:1-3 the Bible provides a demonstration of the types of things that happen when people grow impatient with God. When Abram was 75 years old, God promised Abram that he would receive a land inheritance, that he would be a great nation, and that all of the families of the world would be blessed through Abram. Within a few months, God had done miraculous works in the life of Abram to prove His promises to be legit. In Genesis chapter 15 God even ratified His promises to Abram on His own to prove to Abram that the fulfillment of the promises would be based upon the grace and ability of God, not the performance and righteousness of Abram. Yet in Genesis 16:1-3 the Bible describes Abram and his wife trying to "perform" and help God fulfill His promises because of their impatience.
The Bible says that Abram's wife Sarai had not yet given birth to any children. In Genesis chapter 15, one of Abram's major gripes was that he didn't have an heir to the land that Abram would receive. Abram didn't have a son he could pass on the land that God was going to give. God ratified the promises He made in response to Abram's desire for a child. Therefore, it should have been clear to Abram that God was aware of his desire for a son and was working on it. Nevertheless, Genesis 16:1-3 shows Abram and Sarai making a big mistake because of unbelief. Scripture explains that Sarai thought it would be best if Abram took Hagar, and Egyptian maidservant, and tried to have a baby with her that Sarai could then adopt as her own. Sarai proposed this idea to her husband, and to no surprise, Abram had no objections. Therefore, Sarai gave her maidservant to her husband in order to try and have a baby. What could possibly go wrong in this situation?
The scriptures are clear to provide one important detail in regards to this series of bad decisions from Abram and Sarai. Genesis 16:1-3 informs readers that when these things were taking place, Abram had been living in the land of Canaan for 10 years! Therefore, one must take a few things into consideration. It had been over ten years since God originally made His promises to Abram. It had been 10 years since Abram was 75 years old, thereby making him 85 years old. These truths were likely weighing factors when Abram and Sarai decided to bring Hagar into the mix of their marriage relationship. Both Abram and Sarai were likely thinking that, since it had been 10 years and no child was born, maybe God was waiting on them to respond. Both Abram and Sarai were likely thinking that, since Abram was 85 years old and Sarai was 75 years old, that their window of opportunity to physically be able to bear children was closing rapidly. However, neither Abram nor Sarai considered the power and faithfulness of the almighty God.
Scripture later reveals that God did indeed provide the child He promised in the way He desired to do so. In fact, Abram and Sarai would have to wait another 15 years for that child. The point is that this 10-year reference point that is given in Genesis 16:1-3 is significant because it shows that God takes His time. God is an eternal God and is in no rush. He certainly does not work on our timetable. God is not interested in adjusting His plan and schedule to meet the expectations of people. God promised a son to Abram and God was willing to give Abram a son - in His time, not Abram's time. The scriptures show that God was faithful to His promises in the time that He saw as appropriate. Thus, the mistake of Abram and Sarai was rooted in the fact that their expectations did not match the will of God. The scriptures show Abram and Sarai making foolish decisions that would have consequences that still linger today in the Middle East through violence. Abram and Sarai sought to try and figure out the mind of God, and in their limited understanding of God's true ability, they made a terrible decision that was harmful to their family, to Hagar, and has been harmful to many Jews and Arabs ever since.
Believers today should be diligent to learn the lesson that the scriptures provide. God works in His time and He can take as much time as He wants for two reasons: 1) Because He is God and no one will contend with Him, 2) Because He is all powerful so that circumstances do not affect His ability to accomplish His will. The truth of the matter is that, if God wanted Abram to have a child when he was 4,000 years old, the God would have sustained Abram and Sarai to live for that time, and we'd be hearing about the birth of Isaac in our lifetime today. Though age played an important role in the minds of Abram and Sarai, it was not a restricting factor for the Living God who spoke the universe into existence. Though Abram and Sarai might have desired a child to the extent that they felt entitled to have it at the time of Genesis 16:1-3, they were in no position to feel entitled since God had already made phenomenal promises rooted in abounding grace. The truth is, though it may be hard to digest, is that Abram and Sarai should have been content with the grace they had received in the promises God made, trusting that God is faithful to fulfill them in His time; and that the time God takes to fulfill His promises is equally as important to God's glory as the fulfillment of the promises itself. This is a powerful lesson for every believer to learn even today.