1 Peter 5:8,9

1 Peter 5:8-9 Be sober, be watchful: your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour; whom withstand stedfast in your faith, knowing that the same sufferings are accomplished in your brethren who are in the world.

Expanded Translation

Be calm (sober, self-controlled), be wide awake (watchful and vigilant): Your adversary (enemy, opponent) the devil, as a roaring lion is stalking about, seeking those whom he may gulp down (swallow, devour, gobble), Whom you must oppose with firm faith, knowing (considering, realizing) that the same experiences of suffering are endured by your (Christian) brethren who are in (other parts of) the world.

Be sober

nepho (see discussions under 1 Peter 1:13 and 1 Peter 4:7). Literally meaning not intoxicated, in the New Testament it is used only figuratively: Be free from every form of mental and spiritual drunkennessfrom excess, passion, rashness, etc. In Apostolic usage, it refers to one who is well-balanced or self-controlled. Here (as in 2 Timothy 4:5 and 1 Thessalonians 5:6), Arndt and Gingrich would translate: be self-possessed under all circumstances.

be watchful

gregoreo literally signifies to be awake or watch (Matthew 26:38-40). Metaphorically, as here, to be watchful, vigilant, circumspect; give strict attention to, be cautious. Through carelessness, neglect, and lack of careful attention, our souls can drift away from Christ and become easy prey to Satan. Watch and pray, that ye enter not into temptation (Matthew 26:41).

Both be sober and be watchful are aorist imperatives, indicating sharp commands to be heeded at once.

your adversary, the devil

The term adversary (antidikos) sometimes refers to an opponent in a lawsuit (Matthew 5:25, Luke 12:58; Luke 18:3). This has caused some to believe the devil is called our adversary because he accuses men before God (tries to get a case against us) so God, as judge, may sentence us. However, the word is commonly used in ancient Greek literature (including the Septuagint) to simply indicate an enemy, adversary, or opponent; and, I believe, should so be understood here.

Christ is our friend! All that he does to or for us, he does out of a heart of love and for our good. Not so with Satan! He may, and often does, appear as a friend, BUT HE HAS NOTHING BUT OUR HARM, DAMAGE, AND RUIN in mind. May we never forget this truth!

as a roaring lion walketh about

Many beasts roar or howl when they are hungry. Perhaps we may so understand this phrase. Satan is hungry and eager for souls! Watch out!

seeking whom he may devour

The words walking and seeking are in the present tense, showing constancy of action. You may let down your guard and go to sleep on the job, BUT SATAN DOES NOT! He is at his task of consuming unwary saints at all hours!

His allurements may, and often do, look attractive. But what is his real purpose? To destroy our souls! He seeks those he may gulp down. If Satan's subtlety and slyness are portrayed when he appeared as a serpent (Genesis 3:1), his ferocity and meanness are pictured in this simile of a lion. He is a brutal, ravaging, wild beast! What must we have to ward off such a beast? Peter tells us.

whom withstand stedfast in your faith

The term in (en) may be taken as instrumental: with or by means of faith; or locative: in faith.

Our faith is to be rigid, strong, firm, solid, and immovable, for this is the meaning of stedfast, Homer used this word to describe rocks, God needs people with a rock-like faith!

Equipped with such a trust, we are to resist and oppose Satan. But resist the devil and he will flee from you (James 4:7).

knowing that the same sufferings are accomplished in your brethren who are in the world

Note the Expanded Translation. There are some who believe the brethren here are the Jewish people who were undergoing trials over the world, This is particularly held by those who believe the book was exclusively addressed to Hebrew Christians, the brethren who are in the world referring to non-Christian Jews who were undergoing persecutions at the hands of the Romans.
Whereas the above is a possibility, the whole scope of the verse concerns Christians. The term brethren occurs throughout the book with this significance (1 Peter 1:22, 1 Peter 2:17, 1 Peter 3:8). Realizing that other brethren in other parts of the globe are bearing up under trials similar to our own provides us with spiritual encouragement, (Compare Romans 1:12.)