The whole matter rests on whether Jesus paid for it all - everything - every single sin we ever committed, or will commit. Whether Jesus paid our debt in full - for all time - ensuring that the Law no longer has a hold on us.
Either He did, or He did not.
If He did not, how could we ever be sure that we have sufficiently measured up to His standard of righteousness so that we may feel guaranteed a home in heaven? Whether we are talking about salvation by works or assurance of salvation by works, the only standard is the Law. Therefore, to feel the guarantee that we have a home in heaven by our obedience means that we have our work cut out for us! But, on the other hand, if Jesus fully paid the debt, we have nothing whatsoever to fear.
If Jesus paid it all, I am saved. If He did not, I am in trouble.
No man ever went to hell who trusted in the blood of God's beloved Son. But hell is full of people who trusted in their own self-righteousness.
The devil will do all he can to divert people's attention from the blood of Jesus. It is not once saved, always saved of which the devil is the architect, it is any teaching that will lead to the slightest mistrust in the blood of Jesus shed on the cross. Because Satan know it is the blood that saves - utterly and completely.
What a pity that some Christians will find out when they get to heaven that they were eternally and irrevocably saved from the moment of their conversion, but spent their lives dialoging with the devil over whether or not they were really saved. What a pity that many will find out in heaven there was no need for such insecurity and anxiety. What a pity that some will discover a truth they were afraid to believe on earth, but that would have given them peace, victory, and a basis for solid growth in grace.
Those who think that sinning after their conversion nullifies their salvation will be attaining to morality through fear of punishment (i.e., of losing their salvation). Hence, they try to live moral lives. The mistake that people make is that they call this morality "godliness." It is not that. Men can be moral and godless. Godliness will produce morality, but morality will never produce godliness.
If godliness is rewarded by salvation, then salvation is not free. Living a straight life in order to keep from invalidating our salvation is not godliness. It is morality that is produced exactly the same way the Law produced it - through fear of punishment.
Godliness is living to the glory of the Lord when you realize it is done from the heart, out of gratitude. You cannot live in a godly manner for the glory of God as long as you have your own interest at stake. But when you see that God's justice has been truly satisfied by the death of Jesus and that righteousness is put to your account by faith alone, that is partly what is meant by seeing the glory of the Lord. The result: you have an opportunity to be truly godly. Godliness is never a valid option until we see that we are saved, and kept saved, by the free grace of God. Before that it is something else - morality, fear, carefulness, anxiety, walking a straight line - but not godliness.
As long as there is doubt about your eternal standing in God's grace, there will be an impediment to your having fellowship with the Father.
You cannot have true respect for one who is basing your entire relationship on your own performance. If you feel you are constantly on trial, having to prove yourself, being analyzed, or feeling afraid that you will be cut off the moment you don't live up to some standard, you don't really have respect for that person. You cannot be at ease with someone who is always testing your relationship by how well you are treating him (or her). If your view of God is like that, don't be surprised if you do not have fellowship with Him. You don't really respect Him.
If after all that He has done by sending His Son to die on a cross, He still finds us doubting the validity of His gift, then fellowship with God will be a matter of tension, rather than joy. Fellowship with God is only possible because we are already in the family and cannot be disenfranchised.
Those who doubt their salvation try to live in a godly manner, but it gets them nowhere insofar as joy is concerned. Look at their faces. They have long faces, grim faces, sad faces. They have spent years trying to live up to an (unattainable) standard, and they still haven't done it. People like that are counter-productive - all because they don't take the simplicity of God's word to heart.
All of us have struggled with the simplicity of the gospel. Hoping that we are truly sealed, and that nothing can snatch us from Christ's hand. Struggling to believe His promise that we shall never perish. Time and again we end up saying it is too good to be true. With that in mind, the devil comes along and suggests it is too good to be true. - R.T. Kendall
But it is true.
God meant every word when He inspired Paul to write:
"...neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come, nor height, nor depth, nor any other creature, shall be able to separate us from the love of God , which is in Christ Jesus our Lord." (Romans 8:38-38)
"Any creature" includes ourselves. Once we are adopted into God's family, there is nothing we can do to get out. If it were possible, then Jesus was mistaken when He said, " Whoever hears my word, and believes Him who sent me, has eternal life and will not come into judgment, but has passed from death to life." (John 5:24)
If we could be kicked out, or leave, then the life given was never eternal, we will come under judgment, and pass back into spiritual death.
All the things Jesus said will not happen.
We need to stop trusting in ourselves, and believe God and His word. We are eternally forgiven, can never again come into judgment or condemnation, and can never lose what we didn't earn - God's gift of salvation - based on the finished work of Jesus Christ alone.