The passage where this is found is in Ephesians 4:30: “And do not grieve the Holy Spirit of God, with whom you are sealed for the day of redemption”.
This sealing with the Holy Spirit takes place the moment a person trusts in Christ. The seal is a Person, the Holy Spirit who will live in us forever: “And I will ask the Father, and He will give you another Counselor to be with you forever— the Spirit of truth” (John 14:16-17).
The Holy Spirit is God’s seal of ownership, the sign of a completed transaction. It is the pledge (or down payment) that God will fulfill all His promises to the believer. God paid the entire purchase price so the Holy Spirit can move into the body of the believer, and this guarantee that He will fulfill the rest of the promises He has made.
God indwells the believer (in the Person of the Holy Spirit) and lives there while He fulfills the rest of His pledge). While the believer in Christ has received many of the blessings now (he is born again and has been given eternal life and has become a child of God) he is waiting to receive the completion of his salvation (the glorification of his body and the removal of all the effects of sin). Now the believers is removed from the PENALTY of sin and we are waiting to be removed from the PRESENCE of sin. In the meantime we all have work to do. We now called to represent Christ until he calls us home and fulfills the rest of His promises.
The down payment and the sealing of the Holy Spirit are vitally connected and are both presented in the following verses:
“Now it is God who makes both us and you stand firm in Christ. He anointed us, set His seal of ownership on us, and put His Spirit in our hearts as a deposit (or down payment) guaranteeing what is to come” (II Corinthians 1:21-22).
“And you also were included in Christ when you heard the word of truth, the gospel of salvation. Having believed, you were marked in Him with a seal, the promised Holy Spirit, who is a deposit guaranteeing our inheritance until the redemption of those who are God’s possession—to the praise of His glory” (Ephesians 1:13-14).