If Peter's example is not enough to demonstrate how the full knowledge of one's forever-favored and forgiven state before God can turn a blunt braggart into an assertive and graceful evangelist, consider the example of Paul:
"Though I might also have confidence in the flesh. If any other man thinketh that he hath whereof he might trust in the flesh, I more:
"Circumcised the eighth day, of the stock of Israel, of the tribe of Benjamin, an Hebrew of the Hebrews; as touching the law, a Pharisee;
"Concerning zeal, persecuting the church; touching the righteousness which is in the law, blameless." (Philippians 3: 4-6)
He also openly acknowledged the great evil he did in persecuting Christ's church before his own conversion:
Yet in his ministry, Paul also had the "audacity" to declare his blameless state before assemblies which he preached to throughout his ministry:
"And Paul, earnestly beholding the council, said, Men and brethren, I have lived in all good conscience before God until this day." (Acts 23: 1)
"And herein do I exercise myself, to have always a conscience void of offence toward God, and toward men." (Acts 24:16)
In both verse, before significant assemblies, Paul declares his cleared conscience, his right standing before all.
How else could he do this, but in that he trusted fully in the resurrection power and atonement of Christ's death on the Cross? He declares this in one of his epistles:
"But what things were gain to me, those I counted loss for Christ.
"Yea doubtless, and I count all things but loss for the excellency of the knowledge of Christ Jesus my Lord: for whom I have suffered the loss of all things, and do count them but dung, that I may win Christ,
"And be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith:
"That I may know him, and the power of his resurrection, and the fellowship of his sufferings, being made conformable unto his death;
"If by any means I might attain unto the resurrection of the dead." (Philippians 3: 7-11)
He now has full confidence in the righteousness which comes by faith, Paul has now found himself "in Christ", a place of preeminent power and glory:
"And [God] hath raised us up together, and made us sit together in heavenly places in Christ Jesus:
"That in the ages to come he might shew the exceeding riches of his grace in his kindness toward us through Christ Jesus." (Ephesians 2: 6-7)
"And ye are complete in him, which is the head of all principality and power:
"In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ:
"Buried with him in baptism, wherein also ye are risen with him through the faith of the operation of God, who hath raised him from the dead.
"And you, being dead in your sins and the uncircumcision of your flesh, hath he quickened together with him, having forgiven you all trespasses;
"Blotting out the handwriting of ordinances that was against us, which was contrary to us, and took it out of the way, nailing it to his cross;
"And having spoiled principalities and powers, he made a shew of them openly, triumphing over them in it." (Colossians 2: 10-15)
This same Jesus, glorified and forever honored at the right hand of the Father, is also the same place where each of us who believe on Him are located!
No matter what we have done, no matter how deep our sin, no matter how dirty or vile our past, we can declare boldly that we have no offense with any man, because we have been forgiven of all our sins, we have been made the righteousness of God in Christ, and we sit in glory and honor in Christ at the right hand of the Father:
"Because as he is, so are we in this world." (1 John 4:17)
Christ is under no condemnation; neither are we. Christ is neither despised for past wrongdoings, and so neither are we.
And from this fullness, from this status of eternal forgiveness, we enjoy all other blessings!