16 Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all,
17 ¶ (As it is written, I have made thee a father of many nations,) before him whom he believed, even God, who quickeneth the dead, and calleth those things which be not as though they were.
18 Who against hope believed in hope, that he might become the father of many nations, according to that which was spoken, So shall thy seed be.
19 And being not weak in faith, he considered not his own body now dead, when he was about an hundred years old, neither yet the deadness of Sara’s womb:
20 He staggered not at the promise of God through unbelief; but was strong in faith, giving glory to God;
21 And being fully persuaded that, what he had promised, he was able also to perform.
22 And therefore it was imputed to him for righteousness.
This is the last section of the developed argument by Paul on what is and what is not justification by faith. In Verses 1-4 justification is before God and not of the flesh but by gace. In verses 5-8 Justification of the ungodly without works and by faith. Justification is defined in two aspect - imputation of righteousness and non-imputation of sin.
In Verses 9-13 justification by faith is a completed action before administration of ordinances and therefore is without ordinances and thus non-sacramental. In verses 14-15 justification by faith is without law keeping. In verses 16-22 justification by faith is without personal performance or human assistance but all of grace.
Verse 16 states it is by faith so that it might be "of grace" in order that the promise might be "sure" to "ALL" the seed. In verse 17 Paul limits it to only those things that God can do and must do without human assistance - raise the death, and call things into existence that are not yet existent. Verses 18-22 how it is the power of God that makes sure his promise comes to pass without the assistance of Abaham or Sarah and that justifiying faith is eliminates any kind of personal assistance on their part but rather consists in "being fully persuaded that, what he had promised, he was able also to perform" This alone is the basis for imputation of righteousness (v. 22).
The final verses of chapter four make the direct application to us indicating clearly that "faith" defined as "being fully persuaded that, what he had promised he was also able to perform" is the kind of faith that justifies us in regard to the promise found in the gospel:
23 ¶ Now it was not written for his sake alone, that it was imputed to him;
24 But for us also, to whom it shall be imputed, if we believe on him that raised up Jesus our Lord from the dead;
25 Who was delivered for our offences, and was raised again for our justification
Romans 5:1-2 denies that justification by faith is an ongoing progressive action. Rather Paul uses Aorist and Perfect tense verbs to demonstrate this is a completed action in the past that stands finished presently and that is why we have "peace" now.
Thus faith is defined as "being fully persuaded that what he had promised he was able to perform." Faith is the substance or basis for hope. Justifying faith is in the promise of God as defined in the gospel, this is the substance of hope and thus inseparable from faith. Faith merely lays hold of God's promise as its only baiss for hope. Thus Christ and Christ alone is our "blessed hope" for salvation.