” And you also were included in Christ when you heard the word of truth, the gospel of your 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

God bought us back from eternal death and separation from Him. He is just. God also loved us so much that he personally fulfilled His own requirements for His own justice.

And God sealed the deal as it was prophesied hundreds of years earlier;

 “I will put My Spirit within you and cause you to walk in My statutes, and you will keep My judgements and do them.”

 Ezekiel 36:27 

Anyone whom God has placed His Spirit in belongs to God and He resides in them forever more.

“because of the truth that abides in us and will and will be with us forever.”

2 John 1:2