I agree.
The Holy Spirit in us is the down-payment and guarantee of our future inheritance in Jesus Christ. The Holy Spirit testifies with our spirit that we are one of Christ's Own.
Romans 8:15-17
15 For you have not received a spirit of slavery leading to fear again, but you have
received a spirit of adoption as sons by which we cry out, "Abba! Father!"
16 The Spirit Himself testifies with our spirit that we are children of God,
17 and if children, heirs also, heirs of God and fellow heirs with Christ, if indeed we suffer with Him so that we may also be glorified with Him.
Ephesians 1:13-14
13 In Him, you also,
after listening to the message of truth, the gospel of your salvation-- having also believed,
you were sealed in Him with the Holy Spirit of promise,
14who
is given as a pledge of our inheritance, with a view to the
redemption of God's own possession, to the praise of His glory.
1 Corinthians 1:21-22
21 Now
He who establishes us with you in Christ and anointed us is God,
22 who also sealed us and gave us the Spirit in our hearts as a pledge.
John 6:27
"Do not work for the food which perishes, but for the food which endures to eternal life,
which the Son of Man will give to you, for on Him the Father,
God, has set His seal."
2 Corinthians 5:5
Now He who prepared us for this very purpose is God,
who gave to us the Spirit as a pledge.