Matthew 6:7

"And, when praying, use not vain repetitions, as the gentiles do; for they think that for their much speaking they shall be heard.

Romans 1:21

because, having known God, they did not glorify Him as God, nor did they give thanks; but they became vain in their reasonings, and their senseless heart was darkened.

1 Peter 1:18

knowing that, not with perishable things, with silver or gold, were ye redeemed from your vain course of life handed down from your fathers;

Treasury of Scripture Knowledge

Summary

For the customs of the people are vain: for one cutteth a tree out of the forest, the work of the hands of the workman, with the axe.

General references

Bible References

Customs

Matthew 6:7
"And, when praying, use not vain repetitions, as the gentiles do; for they think that for their much speaking they shall be heard.
Romans 1:21
because, having known God, they did not glorify Him as God, nor did they give thanks; but they became vain in their reasonings, and their senseless heart was darkened.
1 Peter 1:18
knowing that, not with perishable things, with silver or gold, were ye redeemed from your vain course of life handed down from your fathers;

General references

Acts 16:21
and are declaring customs, which it is not lawful for us to receive, or to observe, being Romans.