Peter does not want Christians to stumble over the subject of Christ's return. He encourages them to be steadfast in their faith and remember this fact that the Lord does not view time the same way we do. "A thousand years in Your sight are like a day that has just gone by, or like a watch in the night." (Psalm 90:4) God is outside of time. God's time frame is different than ours. We are finite and we have a finite perspective. God is infinite and He looks at things from an infinite perspective.
God delays Christ's second coming and final judgment because He graciously desires that all people will repent and accept His free gift of salvation through faith in Christ. This is God's heart! Don't mistake God's immense loving patience for slackness/ slowness in the fulfillment of His promise. His motive demonstrates His incredible grace and mercy! The Lord is abounding in love and slow to anger. He is being patient with the ungodly and unrepentant. He is waiting patiently like the father of the prodigal son. We are given more time to reach out to people with the Gospel; do not waste it. Invest in eternity! Some will perish but it is not God's will that they perish. His desire is for all to come to Him, believe in Jesus, be saved, and be with Him for eternity. Jesus died for all. The gift of salvation is available to all. But God will not save us against our will. God also gives us the gift of choice. We can choose Jesus or reject Him. He deliberately keeps giving people more and more time to come to repentance. God has concealed the time of Christ's coming on purpose for His redemptive purpose.
Even though we all deserve God's wrath and condemnation, God our Savior "wants all people to be saved and to come to a knowledge of the truth" (1 Timothy 2:4), "not wanting anyone to perish, but everyone to come to repentance" (2 Peter 3:9b). The purpose of the Messiah’s mission is not to judge or condemn, but to offer the grace of the Gospel, salvation, and eternal life, to people in the world. At His first coming, Christ came to save the world. When He comes again, He will come in judgment upon those who refuse His offer of salvation. Because of God's amazing love, kindness, grace, mercy, and patience, we are offered a pardon and the sentence of condemnation has been delayed. Condemnation is a result of rejecting Jesus (as stated in John 3:18b: "Whoever does not believe stands condemned already because they have not believed in the name of God's one and only Son").