We start with Romans 9:22. I believe the NASB's translation of the passage is very helpful for the understanding of the sentiment. - "So then He has mercy on whom He desires, and He hardens whom He desires. You will say to me then, "Why does He still find fault? For who resists His will?" on the contrary, who are you, O man, who answers back to God? The thing molded will not say to the molder, "Why did you make me like this," will it? Or does not the potter have a right over the clay, to make from the same lump one vessel for honorable use and another for common use? What if God, although willing to demonstrate His wrath and to make His power know, endured with much patience vessels of wrath prepared for destruction? And He did so to make known the riches of His glory upon vessels of mercy, which He prepared beforehand for glory, even us, whom He also called, not from among Jews only, but also from among Gentiles (Romans 9:18-24, NASB)." With that being read, one can clearly see an insight into the reason for the long-suffering of God with regard to the salvation of mankind. While we "were yet sinners" Christ took to the cross for the salvation of all those who believe on Him (Romans 5:8, John 1:12, John 3:16). The reason for such? While God is one to make known His hatred of sin and the deathly consequences of such (cf. Leviticus 10, Hebrews 10:31), He is also one to show His mercy. Therefore, He waiting, even though mankind couldn't care less what His will was, until the perfect time to send the Christ so as to save as many people as possible, snatching them out of the fires of Hell and bringing Him into His wonderful church. - If that isn't a perfect illustration of the reputation of long-suffering, I don't know what is! A further illustration can be seen within the writing of Peter in his first epistle (1 Peter 3:20-21) were the apostle reemphasizes the long-suffering of God in His waiting some 120 years for the flood to occur so that as many people as possible can be saved.
"Lee, those illustrations happened within the Old Testament, but is there a hint of such within the New Testament?" Yes! When writing to Timothy, Paul made the statement which is very familiar to many Christians, "Christ Jesus came into the world to save sinners, of whom I am chief (1 Timothy 1:15)." But are we aware that in the context of that very passage, Paul gives the reason for his acceptance into the role of the apostles? It wasn't because Paul was very well educated, had a large amount of contacts or anything else. It was because he was one of the most horrible sinners to walk the earth, and God wanted everyone to know that He has the power and the willingness to save anyone, regardless of their past. The word which describes this? - "Long-suffering (1 Timothy 1:16)"
I am not sure whether or not Paul would have become a preacher if he had not been declared an apostle and been inspired to do so. However, I have often wondered why so many ex-cons and once horrible people become preachers and are now faithful servants of the Almighty, in my class in preaching school alone this can be evidently seen. I have a strong feeling that Paul would have been a preacher for the same reason that many today are, because we want everyone to know the long-suffering of God is still available today. What better way to teach people than to say, "Look at me, if He can change me He can change anyone!"
Would you be surprised to know that the attitude and reputation of long-suffering, while exuding from the nature of God, is commanded to us as well? I would hope not, in light of the Christian life being an extension of that divine nature as well. But, our faithfulness toward God is to be defined as "long-suffering (Hebrews 6:12)" and because of that we ought to endure both our sins and the sins of others, while attempting to show them the Light just as God has done throughout history. Even though He was waiting and working, He was still convicting and converting.