“And you also were included in Christ when you heard the message of truth, the gospel of your salvation. When you 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, NIVUK
Don’t think it small or insignificant when you experience change when initially coming to faith. It is more than being “saved”.
The presence of the person of the Holy Spirit acts as personal assurance of one’s place in the body of Christ.
It may not be of any practical value to you until a long season of doubt or backsliding but it serves a believer well as a “down payment” of what has not yet been laid ahold of that which has already laid hold of you.