Scripture speaks of certain angels as being "elect." Who are these elect angels? Paul wrote to Timothy.
I charge you in the sight of God, and Christ Jesus, and the elect angels, that you observe these things without prejudice, doing nothing by partiality (1 Timothy 5:21).
The elect angels are most likely those who stayed true to God during the original angelic rebellion. It seems there was a period of time when they were under probation. Their election was revealed by their remaining true to the Lord.
Confirmed In Their Goodness
These angels, who did not stray from the Lord, have been confirmed in their goodness. They are constantly loyal to the Lord. This is a permanent quality of their character.
Elect Believers
Believers are said to be "elect unto obedience."
Peter, an apostle of Jesus Christ, to the elect who are sojourners of the Dispersion in Pontus, Galatia, Cappadocia, Asia, and Bithynia, according to the foreknowledge of God the Father, in sanctification of the Spirit, unto obedience and sprinkling of the blood of Jesus Christ: Grace to you and peace be multiplied (1 Peter 1:1,2).
Like these angels, these believers willingly chose to follow the Lord when given the option. In this sense they are also "elect."
Relate Differently
Because the elect angels do not need any deliverance from sin, as do humans, they are related to Christ differently. He is not their mediator, as He is with humanity. Jesus serves as a mediator between believers and God the Father, He has no such ministry with the "elect angels."
No Will To Choose Evil
It seems that the elect angels, or holy angels, now have no will to choose evil. They made their choice when they did not follow the Devil. This choice seems to be an eternal, irrevocable choice on their part - there will not be another angelic rebellion in the future.
Contrast
The elect angels are in contrast to those who rebelled with the Devil. Judgment is awaiting them.
Then He will say to those at His left, 'You that are cursed, depart from Me into the eternal fire prepared for the Devil and his angels (Matthew 25:41).
These evil angels are cursed for their sin, there is no hope for them.
Summary
Certain angels in Scripture are called "elect." These are the ones who did not rebel against God in the beginning, but rather chose to stay with Him when the rebellion occurred. Like believers, their election was made manifest when they chose to follow the Lord rather than the Devil.