“The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance.”
as some count slackness
We cannot measure God by our standards. God’s delay is a matter of His longsuffering. He has a designated time for dealing with the world. God’s delay does not originate from His unwillingness or impotence to discharge His promise.
but is longsuffering toward us
“Longsuffering” denotes forbearance (Ex 34:6). To possess “longsuffering” is to be long-tempered, to bear with. Longsuffering is a quality of self-restraint in the face of provocation. This quality of character does not hastily retaliate or quickly punish. It is the opposite of anger, especially impulsive anger. Mercy is often associated with this quality (Ex 34:6; Ro 2:4; 1 Pe 3:20). Longsuffering does not surrender to situations, provocations, or failure under trial. This person has patience despite difficulties. God exercises unfathomable patience toward us.
PRINCIPLE:
Patience is the perpetuation of love.
APPLICATION:
God is long-tempered with us. He has infinite longsuffering with those who exercise negative volition toward Him. God does not violate man’s will. He created man as a free agent and respects that agency. God does not usually impose His will on man’s will but gives him time to repent.
It is wonderful that God does not judge us the way we judge others. God deals in facts, not subjective judgments. Men are the opposite: “I don’t have the facts, but I have made up my mind. I don’t like you, so you are irrelevant.” Longsuffering is an attitude of love. This quality does not convey the idea that you would like to let them have it; rather, you hold back because you care about them. No, God’s love takes up the slack.
We will exercise a long temper towards God and others if we operate like Him. Therefore, it is no longer a question of “Lord, you have not provided me with the success I want.” When we love the Lord, we do not ask that question because we know He is faithful to His promises.
One characteristic of love is longsuffering. We find ourselves tolerating things we would not have otherwise allowed. This does not mean we are mindless: “That’s alright, honey, go out and buy that car.” We say, “I want it now.” The Lord says, “It will come in My timing.” Because we love the Lord, we trust Him to give it in His calendar. Patience is the perpetuation of love.

In studying this passage, it appears that the “us” in 3:9b is the believer, NOT the world of unbelievers, and is referring back to verse 8 where Peter exhorts believers to “stop being forgetful in the sphere of” the timing of God’s judgment in verse 7. Some [believers] count the delays of God as denials, and become easily discouraged. The Tribulation saints will, in their distress, say “How long, O Lord, holy and true, until you judge and avenge our blood on those who dwell on the earth?” (Revelation 6:10). Already a couple of years of Daniel’s 70th week are past, and these saints ARE ALREADY MARTYRED and in heaven (6:9), and STILL do not comprehend God’s “longsuffering” even of “earth dwellers”. In fact, His judgments had already begun, and it says “they [the earth dwellers] repented not” four times (cf. 9:20, 21; 16:9, 11).
Could it be, also, that your reference to God’s “will” as God’s plan is correct in that His plan DID NOT PREDESTINE unbelievers to hell, but that they chose it for themselves. Thus, if the Lord rescues and saves anyone, it is by His grace alone. This grace does not NECESSITATE his saving everyone just because His “will” as a plan including selecting out from the world of humanity those who would be His by purchase.
The bottom line of this whole section appears to be aimed at instructing believers concerning the “scoffers” of v.3, not at the scoffers themselves. How we need to trust His ways in these last days of global chaos and rebellion against Him. DK
Don, I agree that the primary argument in context is for believers, however, Peter injects “any” as a parallel to “us,” which, it appears to me, that he is dealing with both the believer and the non-believer. The “any” refers to those who “perish” indicating that they are lost.