“Keep your heart with all diligence,
For out of it spring the issues of life.”  Proverbs 4:23

Jesus explains to His disciples:
“But what comes out of the mouth proceeds from the heart, and this defiles a person.
For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false witness, slander.”  Matthew 15:18-19  
(Read the whole passage for a clear picture Vs. 15-20)

King David knew the tongue could be sinful, we find in Psalm 39:1 he tells of guarding his mouth,
“I said, ‘I will guard my ways,
That I may not sin with my tongue; 
I will guard my mouth as with a muzzle…’”

In Psalm 141:3 David prays (I pray this too.)
“Set a guard, O LORD, over my mouth;
Keep watch over the door of my lips!”

Jesus gives Peter, James and John a warning concerning temptation when He found that they had fallen asleep.  Remember He had asked them to keep watch with Him as He prayed?
“Keep watching and praying, that you may not enter into temptation; the spirit is willing but the flesh is weak.”  Matthew 26:41

Paul warns the Corinthians (since he starts with ‘therefore’ look back to see what he is warning them against):
“Therefore let him who thinks he stands take heed lest he fall,
No temptation has overtaken you that is not common to man.  God is faithful and He will not let you be tempted beyond your ability, but with the temptation He will also provide the way of escape, that you may be able to endure it.”  1 Corinthians 10:11-12 

“Be watchful, stand firm in the faith, act like men, be strong.  Let all that you do be done in love.”  1 Corinthians 16:13 

The strength to stand firm is in Christ’s strength as we see in 
Philippians 4:13,
“I can do all things through Him who strengthens me.”

“Devote yourselves to prayer, keeping alert in it with an attitude of thanksgiving.” Colossians 4:2

Peter tells us in 1 Peter 5:7-9 to cast our care onto the one who loves us,
“Casting all your anxiety upon Him, because He cares for you.
Be sober minded; be watchful. Your adversary the devil prowls around like a roaring lion, seeking someone to devour.
Resist him, firm in the faith, knowing that the same kinds of suffering are being experienced by your brotherhood throughout the world.”

Then here is God’s ever present grace as Peter tells us,
“And after you have suffered a little while, the God of all grace, who has called you to His eternal glory in Christ, will Himself restore, confirm, strengthen and establish you.
To Him be the dominion forever and ever.  Amen”  1 Peter 5:10-11

Watchful, yes!  Fearful no!  Why?
“You are from God…because greater is He who is in than he who is in the world.” 1 John 4:4

And fixing our eye on Jesus, the author and perfector of our faith, we know, 
“And God is able to make all grace abound to you, so that having all sufficiency in all things at all times, you may abound in every good work.”
2 Corinthians 9:8

Hallelujah!