Some people point to the Scriptures stating that believers in Christ are sealed by God with the Holy Spirit as "proof" that believers cannot later reject salvation and be lost. However, this belief is shown to be false when we examine what God has to say about the sealing of His people.

First let's examine the seal used by God with Abraham to identify His people.

"And he received the sign of circumcision, a seal of the righteousness of the faith which he had yet being uncircumcised: that he might be the father of all them that believe, though they be not circumcised; that righteousness might be imputed unto them also"
Romans 4:11

In the Old Testament, the circumcision was a "sign" of the covenant that God has made with Abraham and his seed. Further, Scripture says that it was also a "seal" of the righteousness that had been imputed unto God's people. However, we also know that Scriptures state the circumcision (both a sign and a seal) could be made uncircumcision (no sign, no seal) if you rebelled against God.

"For circumcision verily profiteth, if thou keep the law: but if thou be a breaker of the law, thy circumcision is made uncircumcision."
Romans 2:25

"Circumcision is nothing, and uncircumcision is nothing, but the keeping of the commandments of God."
I Corinthians 7:19

Having a "seal" from God does not preclude one from having to obey His Commandments.

It is also important to understand what a "seal" is. The seal of the Spirit is an earnest of our inheritance in the Lord. The word "earnest" [Greek - Arrhabon] is the equivalent of what in the world you might call earnest money. It is a donwpayment, according to Strong's, representing the sealing of a contract or in God's economy a covenant.

For example, to purchase a house you must enter into a contractual agreement with the owner and give a down payment (earnest money) demonstrating your intent to buy. However, if after entering into the agreement, the owner does not honor the terms of this contract, you have legal grounds to get out of this agreement.

When we enter into salvation, we are creating a covenant (agreement) with God. To seal this agreement, God gives us a down payment (earnest) of His Holy Spirit.

"Who hath also sealed us, and given the earnest of the Spirit in our hearts."
II Corinthians 1:22

"In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whomalso after that ye believed, ye were sealed with that holy Spirit of promise"
Ephesians 1:13

It is also important to note that the actual purchase by God does not take place until the "day of redemption."

"And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption."
Ephesians 4:30

In light of this fact, Jesus' commandments that we "abide" and "endure to the end" become even more clear. Yes, the Holy Spirit is given as a "seal" to those who are saved. So can those who have this seal of the Spirit fall away and lose salvation?

"For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, And have tasted the good word of God, and the powers of the world to come, If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame."
Hebrews 6:4-6