Be ready, for we do not know when the Lord will come for us...( St. John Maximovitch )

Stand fast on spiritual watch, because you don’t know when the Lord will call you to Himself. In your earthly life be ready at any moment to give Him an account. Beware that the enemy does not catch you in his nets, that he not deceive you causing you to fall into temptation. Daily examine your conscience; try the purity of your thoughts, your intentions. 

There was a king who had a wicked son. Having no hope that he would change for the better, the father condemned the son to death. He gave him a month to prepare.
The month went by, and the father summoned the son. To his surprise he saw that the young man was noticeably changed: his face was thin and drawn, and his whole body looked as if it had suffered.

“How is it that such a transformation has come over you, my son?” the father asked.
“My father and my lord,” replied the son, “how could I not change when each passing day brought me closer to death?”
“Good, my son,” remarked the king. “Since you have evidently come to your senses, I shall pardon you. However, you must maintain this vigilant disposition of soul for the rest of your life.”
“Father,” replied the son, “that’s impossible. How can I withstand the countless seductions and temptations?”

Then the king ordered that a vessel be brought, full of oil, and he told his son:

“Take this vessel and carry it along all the streets of the city. Following you will be two soldiers with sharp swords. If you spill so much as a single drop they will cut off your head.”

The son obeyed. With light, careful steps, he walked along all the streets, the soldiers accompanying him, and he did not spill a drop.
When he returned to the castle, the father asked,

“My son, what did you see as you were walking through the city?”
“I saw nothing.”
“What do you mean, ‘nothing’?” said the king.
“Today is a holiday; you must have seen the booths with all kinds of trinkets, many carriages, people animals…”
“I didn’t notice any of that,” said the son. “All my attention was focussed on the oil in the vessel. I was afraid to spill a drop and thereby lose my life.”
“Quite right, my son,” said the king. “Keep this lesson in mind for the rest of you life. Be as vigilant over your soul as you were today over the oil in the vessel. Turn your thoughts away from what will soon pass away, and keep them focused on what is eternal. You will be followed not by armed soldiers but by death to which we are brought closer by every day. Be very careful to guard your soul from all ruinous temptations.”

The son obeyed his father, and lived happily.

Watch, stand fast in the faith, quit you like men, be strong. (I Cor. 16:13).

The Apostle gives Christians this important counsel to bring their attention to the danger of this world, to summon them to frequent examination of their hearts, because without this one can easily bring to ruin the purity and ardor of one’s faith and unnoticeably cross over to the side of evil and faithlessness.
Just as a basic concern is to be careful of anything that might be harmful to our physical health, so our spiritual concern should watch out for anything that might harm our spiritual life and the work of faith and salvation. Therefore, carefully and attentively assess your inner impulses: are they from God or from the spirit of evil? Beware of temptations from this world and from worldly people; beware of hidden inner temptations which come from the spirit of indifference and carelessness in prayer, from the waning of Christian love.
If we turn our attention to our mind, we notice a torrent of successive thoughts and ideas. This torrent is uninterrupted; it is racing everywhere and at all times: at home, in church, at work, when we read, when we converse. It is usually called thinking, writes Bishop Theophan the Recluse, but in fact it is a disturbance of the mind, a scattering, a lack of concentration and attention. The same happens with the heart. Have you ever observed the life of the heart? Try it even for a short time and see what you find.
Something unpleasant happens, and you get irritated; some misfortune occurs, and you pity yourself; you see someone whom you dislike, and animosity wells up within you; you meet one of your equals who has now outdistanced you on the social scale, and you begin to envy him; you think of your talents and capabilities, and you begin to grow proud… All this is rottenness: vainglory, carnal desire, gluttony, laziness, malice-one on top of the other, they destroy the heart.
And all of this can pass through the heart in a matter of minutes. For this reason one ascetic, who was extremely attentive to himself, was quite right in saying that
“man’s heart is filled with poisonous serpents. Only the hearts of saints are free from these serpents, the passions.”
But such freedom is attained only through a long and difficult process of self-knowledge, working on oneself and being vigilant towards one’s inner life, i.e., the soul.
Be careful. Watch out for your soul! Turn your thoughts away from what will soon pass away and turn them towards what is eternal. Here you will find the happiness that your soul seeks, that your heart thirsts for. 

(Translated from Pravoslavnaya Rus) and taken from
ORTHODOX AMERICA, Vol. XIV, No. 2-3, September-October, 1993