You yourselves know very well that the day of the Lord will come like a thief in the night. When they say, ‘There is peace and security’, then sudden destruction will come upon them, as labour pains come upon a pregnant woman, and there will be no escape! But you, beloved, are not in darkness, for that day to surprise you like a thief; for you are all children of light and children of the day; we are not of the night or of darkness. So then, let us not fall asleep as others do, but let us keep awake and be sober; for those who sleep sleep at night, and those who are drunk get drunk at night. But since we belong to the day, let us be sober, and put on the breastplate of faith and love, and for a helmet the hope of salvation. For God has destined us not for wrath but for obtaining salvation through our Lord Jesus Christ, who died for us, so that whether we are awake or asleep we may live with him. Therefore encourage one another and build up each other, as indeed you are doing.
(Church in Wales Lectionary, New Revised Standard Version)
The First Epistle to the Thessalonians was written by St Paul, probably from Corinth in about 49-51 AD, so this would be less than 20 years after the death and resurrection of Jesus. The Christians in Thessalonica were very new Christians, Paul having only been with them for a few weeks. Local Jews had been stirred to opposition and Paul keeps in contact with them to support them. He also calls them to be awake and alert so that when the Lord Jesus returns He will find them waiting and ready for Him.
During the Second World War the image of a little person peeping over a wall became well known as a Lert, standing for "Be Alert". Lerts appeared everywhere to remind the people to watch out for security breaches that might affect the lives of people.
In Advent the theme of "Keep awake" and "Be alert" is strong for us as well. We are reminded that the 'Day of the Lord' will come. It may not come tomorrow, but it will come some time, and this day will be one of Judgement. But Paul reminds us that it should not worry us if we live the kind of life that God calls us to live - a life of faith, of love, and of hope.
Heavenly Father,
may we stay awake and alert this Advent
as we move towards the celebration
of the birth of Your Son,
remembering that He said He would return.
May we look again at ourselves -
at the strength or weakness of our faith,
at the love we show for You
and for those around us,
May we also look forward with confidence.
Amen.
You might like to look at these verses from the Bible about being Awake: