Matthew 4:10

Then saith Jesus to him, Be gone, Satan! for it is written, "Thou shalt worship the Lord thy God, and him only shalt thou serve."

Luke 4:8

And Jesus answering said to him, It is written, "Thou shalt worship the Lord thy God, and him only shalt thou serve."

Matthew 6:24

No one can serve two masters; for either he will hate one, and love the other; or else he will cleave to one, and despise the other. Ye cannot serve God and mammon.

Matthew 15:8

"This people honoreth me with their lips, but their heart is far from me.

John 4:24

God is a spirit; and they who worship must worship in spirit and in truth.

Treasury of Scripture Knowledge

Summary

And Samuel spake unto all the house of Israel, saying, If ye do return unto the LORD with all your hearts, then put away the strange gods and Ashtaroth from among you, and prepare your hearts unto the LORD, and serve him only: and he will deliver you out of the hand of the Philistines.

Bible References

Prepare

Matthew 15:8
"This people honoreth me with their lips, but their heart is far from me.
John 4:24
God is a spirit; and they who worship must worship in spirit and in truth.

Serve him

Matthew 4:10
Then saith Jesus to him, Be gone, Satan! for it is written, "Thou shalt worship the Lord thy God, and him only shalt thou serve."
Matthew 6:24
No one can serve two masters; for either he will hate one, and love the other; or else he will cleave to one, and despise the other. Ye cannot serve God and mammon.
Luke 4:8
And Jesus answering said to him, It is written, "Thou shalt worship the Lord thy God, and him only shalt thou serve."