This passage of scripture is extraordinarily clear. Jesus is very blatant, when he states "Not everyone who calls me 'Lord, Lord' will enter the Kingdom of heaven, but only those who do what my Father in heaven wants them to do."
This is a reminder that, calling yourself a Christian, isn't sufficient. Each of us needs to look at the way we are living, and see if our actions line up with our declarations.
James 1:22-25, compares this type of self-reflection as someone who looks into a physical mirror. It reads as follows:
Do not deceive yourselves by just listening to his word; instead, put it into practice. If you listen to the word, but do not put it into practice you are like people who look in a mirror and see themselves as they are. They take a good look at themselves and then go away and at once forget what they look like. But if you look closely into the perfect law that sets people free, and keep on paying attention to it and do not simply listen and then forget it, but put it into practice--you will be blessed by God in what you do.
-James 1:22-25
This portion of scripture is a great reminder. However, the entire chapter is very insightful. It talks about spiritual trials, testing and temptation.
So, it's not hard to find lots of scripture that reminds us that, a relationship with Jesus, isn't something that works like being on autopilot. As Christians, we have to always be conscious that we're in a spiritual war. We're not only at war with all of the bad and sinful things that take place in this fallen world, but are, also, constantly at war with our own struggles; which take place inside of us. We must guard our hearts, and protect our minds; all the while remembering that we were, first, naturally born as sinners.
It's true that, once we became Christians, we were born again, and received the Holy Spirit; who enables us to obey Christ. However, we still have a sinful nature, that now fights against our new nature, which has been given to us.
Paul wrote extensively about the spiritual struggle in Romans chapter 7. If you're a Christian, and you read it, you'll find that it's very relatable; which shouldn't be surprising. However, I would guard against choosing to only read that chapter. This is because, although it does a great job explaining the struggle that we have, it's possible for a person to accept that struggle, with a mind of defeat. This can be dangerous, because it can incentivize a person to be more accepting of any sins that they may be tempted to commit.
This is a serious danger. I can't remember, exactly, where I saw it. However, I remember a young man, who professed to being a Catholic; talking about how he enjoys being a Catholic, because he can sin all weekend, and then just go to confession, and everything is fine.
This is, clearly, the wrong attitude to have, and no one is fooling God, should they choose to subscribe to it.
As we've already read, giving in to sin, isn't an option for us, as followers of Christ. As Christ, himself, warned, we can't just call him "Lord", but then choose not to obey him.
This leads me to one chapter, in the Bible, that I find to be the most terrifying, but one that also offers the most assurance. It's Hebrews Chapter 6. It talks about those who abandon their faith.
The first half of this chapter is absolutely horrifying; at least it is, to me. I'm referring to verses four through eight. In those verses, it talks about the terrible dangers of abandoning the faith, and that, if a person makes this choice, there doesn't seem to be much hope of coming back from it.
However, the second half, offers an extreme promise to Christians. This is a promise which comes from the sovereign God of the universe. I'm referring to verses nine through twenty. In these verses, we read that God's promise to complete a person's salvation, is of the same calibur as his special promise to Abraham. It's a vow, that he has made, in his own name. This vow offers us the utmost assurance. However, it only applies to those who are his; to those who have made that genuine choice to follow him.
Here's what we read in Hebrews 6:4-20:
For how can those who abandon their faith be brought back to repent again? They were once in God's light; they tasted heaven's gift and received their share of the Holy Spirit; they knew from experience that God's word is good, and they had felt the powers of the coming age. And then they abandoned their faith! It is impossible to bring them back to repent again, because they are again crucifying the Son of God and exposing him to public shame.
God blesses the soil which drinks in the rain that often falls on it and which grows plants that are useful to those for whom it is cultivated. But if it grows thorns and weeds, it is worth nothing; it is in danger of being cursed by God and will be destroyed by fire.
But even if we speak like this, dear friends, we feel sure about you. We know that you have the better blessings that belong to your salvation. God is not unfair. He will not forget the work you did or the love you showed for him in the help you gave and are still giving to other Christians. Our great desire is that each of you keep up your eagerness to the end, so that the things you hope for will come true. We do not want you to become lazy, but to be like those who believe and are patient, and so receive what God has promised.
When God made his promise to Abraham, he made a vow to do what he had promised. Since there was no one greater than himself, he used his own name when he made his vow. He said, "I promise you that I will bless you and give you many descendants." Abraham was patient, and so he received what God had promised. When we make a vow, we use the name of someone greater than ourselves, and the vow settles all arguments. To those who were to receive what he promised, God wanted to make it very clear that he would never change his purpose; so he added his vow to the promise. There are these two things, then, that cannot change and about which God cannot lie. So we who have found safety with him are greatly encouraged to hold firmly to the hope placed before us. We have this hope as an anchor for our lives. It is safe and sure, and goes through the curtain of the heavenly temple into the inner sanctuary. On our behalf Jesus has gone in there before us and has become a high priest forever, in the priestly order of Melchizedek.
-Hebrews 6:4-20