Miracle Workers.

On that day many will say to me, ‘Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?’  And then will I declare to them, ‘I never knew you; depart from me, you workers of lawlessness.’ Matthew 7:22

Then that lawless one will be revealed whom the Lord will slay with the breath of His mouth and bring to an end by the appearance of His coming. that is, the one whose coming is in accord with the activity of Satan, with all power and signs and false wonders,  and with all the deception of wickedness for those who perish, because they did not receive the love of the truth so as to be saved."
2 Thessalonians 2:8-10

How can we tell if miracles or mighty works are from God or Satan?
These first two verses tell us these demons are lawless. In other words, they do not keep the law of God. 
If you see a man, woman, or an angelic being work miracles and many people are following him, you can know if they are from God if they follow the law of God. 

If these people say wars and killing are needed, if they say we must punish those who don't believe as they do, if they have no love in their hearts, if they indulge in sexual sin and greed for money and possessions, then we can know they are not from God.

Jesus told us, “Beware of false prophets, who come to you in sheep’s clothing but inwardly are ravenous wolves.You will recognize them by their fruits. Are grapes gathered from thorn bushes, or figs from thistles? Matthew 7:15

Fruits: "But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law." Galatians 5:22,23

If they do not have these fruits in their lives then they are false prophets or messengers.

"Now the Spirit expressly says that in later times some will depart from the faith by devoting themselves to deceitful spirits and teachings of demons..."  1 Timothy 4:1

"But realize this, that in the last days difficult times will come. For people will be lovers of self, lovers of money, proud, arrogant, abusive, disobedient to their parents, ungrateful, unholy, unloving, irreconcilable, malicious gossips, without self-control, brutal, haters of good, treacherous, reckless, conceited, lovers of pleasure rather than lovers of God, holding to a form of godliness, although they have denied its power; Avoid such men as these." 2 Timothy 3:1-5

So, these miracle workers will have a "form" of godliness but do not have God's power in their lives. They say they are Christians, but they are not.

The largest deception will be when Satan transforms himself into an angel of light. 

"And no wonder, for even Satan disguises himself as an angel of light. Therefore it is not surprising if his servants also disguise themselves as servants of righteousness, whose end will be according to their deeds." 2 Corinthians 11:14, 15

Jesus also said, "For false Christs and false prophets will arise and will show great signs and wonders, so as to mislead, if possible, even the elect. See, I have told you beforehand." Matthew 24:24, 25

Jesus said, "See, I've told you ahead of time." We have his warning and his method on how to recognize his true followers.

Building Your Life.

Jesus said, "Therefore everyone who hears these words of mine and puts them into practice is like a wise man who built his house on the rock.The rain came down, the streams rose, and the winds blew and beat against that house; yet it did not fall, because it had its foundation on the rock. "
 Matthew 7:24,25

The rock represents Jesus and the house represents your life.

"For they drank from the spiritual rock that traveled with them, and that rock was Christ." 1 Corinthians 10:4

This is an article by Charles Spurgeon on this subject:

Hearing is not enough; we must do these sayings. The doing hearer has built his house with a stable foundation; the wisest and safest., but also the most expensive and toilsome thing to do. 

Trials come to him. His sincerity and truthfulness do not prevent his being tested. From above and from beneath, and from all sides the trials come: rain, floods and wind. All these beat upon the house. The tests become so severe that nothing can save the building unless it be the strength of its foundation. Because the chief support is so immovable the entire structure survives. "It fell not."

The house may have suffered damage here and there, and it may have looked very weather-beaten; but "it fell not." Let the Rock of Ages be praised if, after terrible tribulation, it can be said of our faith, "It fell not; for it was founded upon a rock."

Jesus said, "And everyone who hears these words of mine and doesn't put them into practice is like a foolish man who built his house upon the sand; and the rain descended, and the flood came and the winds blew, and beat upon that house; and it fell, and great was the fall of it." Matthew 7:26,27

Spurgeon:

 He built his house, he was practical and persevering and did not begin and leave off before completion. Yet though he was industrious, he was foolish. No doubt he built quickly, for his foundation cost him no severe labor; his excavations were soon made, for there was no rock to remove: he built his house upon the sand. But trials come even to insincere professors of Christianity. Are we not all born to trouble? The same kind of afflictions come to the foolish as come to the wise, and they operate in precisely the same way; but the result is very different. "It fell." Its chief weakness was underground, in the secret place of the foundation: the man "built his house upon the sand." His fundamentals were wrong.

The crash was terrible; the sound was heard afar: "great was the fall of it."