2:4-6 Who are the angels referred to here and when did they sin?
2:4-6 Who are the angels referred to here and when did they sin?
These are fallen angels who rebelled against God and sinned in the days of Noah. Jude also refers to them in his epistle (CP Jude 6-7).
The angels' first estate which they did not keep was their original status in God's order - the exalted position they held in heaven above earthly humans (CP Psa 8:4-5; He 2:6-7).
The habitation the angels left was their heavenly abode; the strange flesh they went after were earthly women, and the sin they committed was fornication.
These angels abandoned their heavenly abode and became sexually involved with earthly women, producing the giants of the Old Testament and corrupting all flesh, which precipitated the flood that destroyed everyone on earth except Noah and his family (CP Gen 6:1-8, 11-13, 17 with 1 Pe 3:18-20).
The "sons of God" in Gen 6:2, the "spirits in prison" in 1 Pe 3:19, the "angels that kept not their first estate" in Jude 6, and the "angels that sinned" in 2 Pe 2:4 all refer to the same angels.
Why they have been chained up in prison and others are free to work with Satan in the earth in the New Testament is not explained in scripture (See also comments on Mt 12:38-40, Eph 4:9, He 9:27 and 1 Pe 3:18-20 (A) and (B)).