The first few verses here tells us that Abram was wealthy in livestock, gold and silver. If you choose to follow God, it doesn't meant you will be rich, but you will have all your needs met, God will provide for you. Abram had all he needed to stay put and live a very comfortable life, yet he chose to leave to go where God was calling him. Gods plan for us always needs to come before our comfort in our current situation. Lot also went with Abram and he too had many flocks and herds and tents. Between all that Lot had and all that Abram had, it was too much to dwell in one spot initially without satan causing strife, the herdsman began to argue and it trickled up to Lot and Abram. Instead of all coming together to work as one and eliminate the strife, they decided to separate. Abram knew they needed to keep the peace between all of them, so he told Lot to choose where he wanted to reside first, and then Abram chose to go further away from that spot so they each had their own room to grow into the land in peace. Lot chose what appeared to visually be the better land that had water, but spiritually his land was right next to Sodom, a sinful place full of wicked men. This is a good example why we should always seek God before making decisions. What might seem like the best option for us may have underlying things that wont be good for us that we just cant see with the plain eye. But God sees all, which is why its always best to seek His answer rather than decide on your own based off of the little you can see. The choices they made shows us a lot about their character. Lot chose the best land despite the fact that it was neighboring an evil and sinful place, he chose to go off of looks of the land rather than to seek Gods advice. He didn't realize the temptations that would come with living close to Sodom and the harm that could be done. He just thought about what was best for himself with what appeared to be the best land and went for it. Abram was selfless when he told Lot to choose first.
After they chose their land God said to Abram that God has given all this land to Abram and his descendants, and that God would make Abrams descendants as the dust of the earth. God told Abram that if man could number the dust of the earth, then your descendants could also be numbered. God knows what our thoughts our and sees our hearts, He knew Abram would follow God and do as He commanded, and God saw Abrams selflessness and rewarded him. God sees the struggles or situations we face as well, and He rewards us when He sees us seeking Him for the answers and following what He would want from us. Our focus needs to be on God, and He will take care of the rest for us.