Many people want to know: “How can I know that I am a Christian?” It’s a valid and important question.
Actually, the Bible has a vast amount of information about the subject. John the Apostle wrote his first epistle to his “children” so that they might know that they had eternal life (1 John 5:13). When you do a study of this epistle, you can make a quick list of all the ways that you may know that you have eternal life. It only makes sense. Jesus came that we might have life and have it to the full (John 10:10).
Paul dealt with this issue as well. He reminded early believers that God the Holy Spirit had worked in their lives and that they had been sealed by the Holy Spirit until the day of redemption (Ephesians 4:30).
Paul had earlier in the epistle made it clear about the seal. He told the Ephesians that they had heard the Gospel and believed and having believed in Christ were marked in Him with a seal, the promised Holy Spirit. Authorities attached a seal to guarantee the genuine character of a document or a person. So, the Holy Spirit testifies that we are the genuine article–the children of God. The Holy Spirit Himself is the deposit which guarantees our inheritance (Ephesians 1:13-14).
What a powerful picture. The transaction–our hope in Christ–is guaranteed by the down payment of the Holy Spirit! We can be sure that we have eternal life because we have received the promised Holy Spirit. His presence with us assures us that we belong to Him, and He keeps us as He promised.
Therefore, take heart. Your labor in the Lord is not in vain. In the same way that you received the Holy Spirit, you will also experience the final redemption in Christ. No wonder Jesus said: Lift up your heads, your redemption is close at hand (Luke 21:28).