1 Thessalonians 3:5

For this reason, when I could stand it no longer, I sent to find out about your faith. I was afraid that in some way the tempter might have tempted you and our efforts might have been useless.

when I could stand it no longer
1 Thessalonians 3:1 So when we could stand it no longer, we thought it best to be left by ourselves in Athens.

I sent to find out about your faith
1 Thessalonians 3:2 We sent Timothy, who is our brother and God's fellow worker in spreading the gospel of Christ, to strengthen and encourage you in your faith, ...

I was afraid that in some way the tempter might have tempted you
Matthew 4:3 The tempter came to him and said, "If you are the Son of God, tell these stones to become bread."
Mark 4:15 "Some people are like seed along the path, where the word is sown. As soon as they hear it, Satan comes and takes away the word that was sown in them."
2 Corinthians 4:4 The god of this age has blinded the minds of unbelievers, so that they cannot see the light of the gospel of the glory of Christ, who is the image of God.
Ephesians 6:16 In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one.

and our efforts might have been useless
Galatians 2:2 I went in response to a revelation and set before them the gospel that I preach among the Gentiles. But I did this privately to those who seemed to be leaders, for fear that I was running or had run my race in vain.
Philippians 2:16 ... as you hold out the word of life--in order that I may boast on the day of Christ that I did not run or labor for nothing.

NOTES:
The tempter:
supreme among evil spirits - John 16:11; Ephesians 2:2
can affect the physical - 2 Corinthians 12:7
can affect the spiritual - Matthew 13:37-39; Mark 4:15; 2 Corinthians 4:4
tempts Jesus - Matthew 4:1-11
tempts Jesus' servants - Luke 22:3; 1 Corinthians 7:5
hinders missionary work - 1 Thessalonians 2:18
has already been defeated - Colossians 2:15
we need not be overwhelmed by him - Ephesians 6:16
his final overthrow is certain - Revelation 20:10
Read Romans 8

Scriptures taken from the Holy Bible, New International Version® NIV®, Copyright© 1973, 1978, 1984 by International Bible Society. Used by permission. All rights reserved worldwide.