"Tribulation is also the Cross applied to the flesh in daily life" - exactly. Does the "broad way" group want to go the way of the cross? No, they think of it as foolishness. That same foolishness is the narrow way however. Mat 7:14 Because strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it.
The narrowness of the narrow way is decribed further down in its own context. These are the ones that also thought they have entered, but by the broadway access: Matthew 7:21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven. Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
So what is the dividing line, which ones are unknown to Jesus? - They that work iniquity. Also called lawnessness. They confess his name, are engaged in activities dedicated to Jesus, yet they themselves are overcome by their sin nature. Therefore they may understand Romans 8 intellectually regarding the walk in the Spirit, but they not really walk in it, or are seduced by a counterfeit spirit that convinced them they would be walking by grace in the Holy Spirit. Lawlessness also indicates contempt for the law of God and the commandments of Jesus, so they are not only lawless but also disobedient.
Same/related warning as in Mat 7:22 here in Jude 1:4 For there are certain men crept in unawares, who were before of old ordained to this condemnation, ungodly men, turning the grace of our God into lasciviousness, and denying the only Lord God, and our Lord Jesus Christ.
How do they deny our Lord Jesus Christ? By distorting grace to be what it's not, a lifestyle in sin and breaking the commandments of God. How do we know that? 1 John is all about verification tests, so we know who we are in reality:
1 John 3:7 Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous. He that committeth sin is of the devil; for the devil sinneth from the beginning.
That is like a snapshot verification of "status report of today" - not an attainment plan, just like this one, snapshot proof of knowing Jesus: 1 John 2:3 And hereby we do know that we know him, if we keep his commandments
It comes down to how we regard personal sin in our own life, if you always excuse your own sins and never repent, you are in trouble and don't even know it. We find His grace again in repentance. And are given His Spirit of power to turn at His reproof. Whenever you are convicted of sin or false ways you previously regarded as truth - and not turn at His reproof, you are avoiding the cross and invest in your personal iniquity account instead. What would leave you in a state of:
2 Tim 3:5 Having a form of godliness, but denying the power thereof: from such turn away.
They deny the cross and the Holy Spirit power to overcome sin and every false way. Their form of godliness is an imitation.
1 Cor 1:18 For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God.
That is the overcomer statement, they are the ones that accept the cross and cooperate with the Holy Spirit. The cross is more painful because you have to give up your pride, ignorance and vanity, however you then actually are walking in the Romans 8 Holy Spirit and not in the flesh or traditions of men.