A spiritual kingdom requires a spiritual nature, and in order to the acquisition of that the natural man must be regenerated (born again), divinely regenerated, for the creature can no more quicken himself than he can give himself a natural being. Why not? Because regeneration is no mere outward reformation, process of education, or even religious cultivation. No, it consists of a radical change of heart and transformation of character, the communication of a gracious and holy principle, producing new desires, new capacities, a new life. The new birth is absolutely imperative, but this is the work of the Spirit of God from the very nature of the case. Birth altogether excludes the idea of any effort or work on the part of the one born, hence it is written 'It is the Spirit that quickeneth; the flesh profiteth nothing' (John 6:63).
By his apostasy man lost his holiness, is wholly corrupt and under the dominion of dispositions and lusts which are directly contrary to God. The corruption of man's being is so great and entire that he will never truly repent unless and until he is supernaturally renewed by the Holy Spirit.
It is crystal clear that a mental assent to the Gospel will save no one, nor will a mere empty profession of faith in Christ. So many flatter themselves that they are born again because they have been baptized, joined some 'church of their choice' received the Lord’s supper who do not have a keen and humbling sense of sin. Professing to be Christians, they are filled with a vain and presumptuous confidence that all is well with their souls, deluding themselves with hopes of mercy while continuing to live in a course of self-will and self-pleasing
For salvation, 'repentance unto life' is just as necessary as is faith in our Lord Jesus Christ. No sinner was ever pardoned while he remained impenitent, while he remained in rebellion against God and His authority, and without submitting himself whole-heartedly to His Lordship. This involves the realization in his heart, wrought therein by the Holy Spirit, of 'the sinfulness of sin' (Rom 7:13), of the awfulness of ignoring the claims of God and of defying His authority. Repentance is a 'holy horror and hatred of sin, a deep sorrow for it, a contrite acknowledgment of it before God, and a complete hear forsaking of it.
To exhort sinners to be saved by 'Accepting Christ as their Saviour' without pressing upon them the imperative necessity of repentance is dishonest, and is to falsify God’s terms of salvation, for 'Except ye repent ye shall all likewise perish' (Luke 17:3) is the Divine dictum. The sinner must either repent or perish, there is no other alternative. And since 'All have sinned' (Rom. 3:23) all therefore need to 'repent and believe the Gospel' (Mark 1:15) else they will be 'punished with everlasting destruction' (2Thess. 1:9). To delay repentance then is most perilous.