Can't Leave it Behind
There are things in life that you can't leave behind. You can't travel overseas without a passport. There are good reasons for this. The passport says that you are recognized and approved by your government to travel overseas. It states the name, sex, date of birth, and place of birth. Sometimes getting a passport happens quickly. Other times, you have to wait for processing to take longer than normal. You have to work within the system.
Just like you have to work within the system on earth, you have to work within God's system to get to Heaven. Traveling to Heaven also requires a passport. If you skip the first step, you will not complete the journey. This step is salvation. Adam and Eve placed their desires above God's and choose to do what He told them not to. It's been all downhill since then. Everyone of us has sinned.
But from the beginning, God has had a plan. He made a way to cover the sins we commit. The mess we made required God's help to overcome. So, He sent His son to take our sins off of us and on Himself. He died as a sacrifice to cover what we could not. God wants you to accept salvation and join Him in Heaven.
You have to work within God's rules, but He has already done the hard work. God's rules are that He calls you to salvation and you accept the sacrifice He made for you. This rule also involves repentance. That is you turn away from ungodly lifestyle, and live according to God's plan.
On the one hand, this is completely free. You owe God no money for what He has done. On the other, it costs you everything. When you follow God's plan, you give up your own hopes and desires. There will be things you used to do that you can no longer do. That will vary by person, but God may tell you no longer date the woman you are dating. You may have to give up some of your money. Some habits will have to go. The choices may be hard, but you have to weigh this in the long run. What you are giving up doesn't compare to what you are gaining. You gain eternity at the cost of a few temporary activities.
You decide to accept the sacrifice. You respond to God's call. Now, you have a passport from God for eternity. No one can steal it from you. You can't accidentally lose it or misplace it. But you could choose to give it up. You can choose to lay down the passport and go back to your old ways. But if you give up your salvation, you will not experience Heaven.
Some people say that you have to do other things after salvation to get into Heaven. They say you have to be baptized, attend church and tithe. This is not the case. All of those things are good and will allow you to grow in your new life, but not one is required for Heaven. The only one required is salvation. Just like you can't get on a plane to Scotland without a passport, you can't get to Heaven without being saved.