1 Forasmuch then as Christ hath suffered for us in the flesh, arm yourselves likewise with the same mind: for he that hath suffered in the flesh hath ceased from sin;
2 That he no longer should live the rest of his time in the flesh to the lusts of men, but to the will of God.

[As Christ hath suffered for us...arm yourselves...with the same mind] He is your proper pattern; have the same attitude he had; the same forgiving spirit, with meekness, gentleness, and complete self possession.

[He that hath suffered in the flesh hath ceased from sin.] One of the most obvious changes when a person becomes a Christian is a change in behavior. He is certainly capable of sin but chooses to conform to God's will rather than to the surrounding culture. In many cases this results in a certain amount of suffering here on Earth while still in the flesh.

3 For the time past of our life may suffice us to have wrought the will of the Gentiles, when we walked in lasciviousness, lusts, excess of wine, revellings, banquetings, and abominable idolatries:

[The time past of our life] Before they became believers. Peter was writing to Christians (both Jewish and Gentile believers) who were dispersed among the Gentiles, therefore were immersed in the Gentile culture which was renowned for
A. Lasciviousness: lechery, lewdness and impurity.
B. Lusts: strong irregular appetites and desires.
C. Excess of wine: from two Greek words, wine and to be hot. To be inflamed with wine.
D. Revellings: Boisterous, ill mannered behavior.
E. Banqueting: Drunken and lacivious feasts.
F. Abominable idolatries: the abominations practiced at their idol feasts where they not only worshipped the idol but did so with the most impure, obscene, abominable rites.

4 Wherein they think it strange that ye run not with them to the same excess of riot, speaking evil of you:

[Wherefore they think it strange] They wonder and are astonished at you that you renounce their way of life and adopt godly behavior, the value of which they cannot see.

[Speaking evil of you] The change in you makes them uncomfortable so they become defensive and attempt to discredit you and the source of your changed mind. The literal translation of The Greek word used here is Blaspheme. To speak evil of God.

5 Who shall give account to him that is ready to judge the quick and the dead.

[Who shall give account to him] You, who are evil spoken of, understand that there is a scorekeeper before whom every person shall stand and be judged for the actions of this life. Those who are so quick to condemn your manner of living do not understand this fact. They are spirtually dead, not having been born again, and so are unconscious toward spiritual matters.

[Him that is ready to judge the quick and the dead] Who will most certainly judge both the spiritually alive and the spiritually dead. The God of love is also the God of righteousness and justice, else there would have been no need for him to pay such a price for our redemption.

6 For for this cause was the gospel preached also to them that are dead, that they might be judged according to men in the flesh, but live according to God in the spirit.

[For this cause was the gospel preached also to them] Because the spiritually dead are unaware of the peril they face, God has assigned to believers the task of warning them. Acts 1:8.

When they are converted they will also be subject to harsh judgement by this world, but their eyes will be upon Christ. So the cycle will continue until the Lord returns.

With regard to the judgement mentioned in verse 5, the following is a summary of what the Bible says about the final judgement of individuals.

Christ will judge the believers according to their works. When Christ returns for his own, John 14:1-3, he will judge them according to their works, not to determine their salvation -- for their sins are forgiven and remembered no more, Hebrews 10:9-17, -- but to determine reward for service rendered 2 Corinthians 5:1-10, 1 Corinthians 3:8-17.

God will judge all unbelievers according to their works. The dead (in this case, those who are without spiritual life) will stand before God to be judged according to their works, not to determine their salvation -- for they are already lost, John 3:18, -- but to determine additional punishment according to the life which they lived. Revelation 20:11-15. Their fate will be the lake of fire because their names will not be found in the book of life.

The ultimate judgement is not made by God, but by ourselves. Please take time to study the first 18 verses of John chapter 3, especially John 3:16. John 3:1-18.
Are you a believer? Tell God about it. He already knows but will be delighted to hear it from you. Luke 15:3-7.