14 So then, dear friends, since you are looking forward to this, make every effort to be found spotless, blameless and at peace with him. 15 Bear in mind that our Lord’s patience means salvation, just as our dear brother Paul also wrote you with the wisdom that God gave him. 16 He writes the same way in all his letters, speaking in them of these matters. His letters contain some things that are hard to understand, which ignorant and unstable people distort, as they do the other Scriptures, to their own destruction.
Today, as Peter finishes his second letter to the early church, he uses this opportunity to challenge them in their own relationship with The Lord. He uses the term again, "make every effort". People get nervous about this saying as they fear this might lead people back to a "works mentality". Meaning our relationship with God is based on what we do for him. But in this context, Peter is writing in regard to Jesus' return. He is getting them ready for the day when Jesus would return and that they would be prepared. Meaning that they would be doing what He had commanded them to do before he left.
Since the false teachers were teaching a heresy that once someone was forgiven, they could do whatever they pleased. He doesn't want them to fall into that trap. And he issues them a warning by saying, "remember that our Lord's patience means salvation." Meaning God was patient with sinners waiting for them to repent, but they as believers have already been saved. Therefore they would be held accountable for the teaching they had been given.
Then he mentions Paul's letters, which authenticate that they were in circulation when Peter wrote. Note Paul's letters focused on the concept of "cheap grace" as well. He writes this in Romans 6,
6 What shall we say, then? Shall we go on sinning so that grace may increase? 2 By no means! We are those who have died to sin; how can we live in it any longer?
15 What then? Shall we sin because we are not under the law but under grace? By no means! 16 Don’t you know that when you offer yourselves to someone as obedient slaves, you are slaves of the one you obey—whether you are slaves to sin, which leads to death, or to obedience, which leads to righteousness?
Notice he says twice, "by no means". It as if he is saying, "may it never happen". So we can see Peter and Paul write similar messages in their letters. Both Paul and Peter wanted the disciples to be ready when Jesus chose to return. Although they had been saved by grace and not by works, he still wanted them to live a life worthy of their calling and be spotless, blameless and at peace with him.
Since we likewise, do not know when Jesus is going return, it might be wise for us to heed Peter's advice as well!