What part does the Holy Spirit play in salvation?

The Holy Spirit plays a key role in salvation by convicting people of sin, leading them to repentance, and sealing them as children of God when they believe in Christ.

In Him you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also, having believed, you were sealed with the Holy Spirit of promise, 14who is the guarantee of our inheritance until the redemption of the purchased possession, to the praise of His glory. (Ephesians 1:13-14)
Therefore I make known to you that no one speaking by the Spirit of God calls Jesus accursed, and no one can say that Jesus is Lord except by the Holy Spirit. (1Chrointians 12:3)

But if the Spirit of Him who raised Jesus from the dead dwells in you, He who raised Christ from the dead will also give life to your mortal bodies through His Spirit who dwells in you. (Romans 8:11)

Not only does the Holy Spirit convict people of sin and lead them to God, but He also guides prayer, helps them understand God’s Word, gives them wisdom, serves as a counselor and advocate in the lives of believers in Jesus Christ.

But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all things that I said to you. (John 14:26)

Likewise the Spirit also helps in our weaknesses. For we do not know what we should pray for as we ought, but the Spirit Himself makes intercession for us with groanings which cannot be uttered. (Romans 8:26)

Now we have received, not the spirit of the world, but the Spirit who is from God, that we might know the things that have been freely given to us by God. 13These things we also speak, not in words which man’s wisdom teaches but which the Holy Spirit teaches, comparing spiritual things with spiritual. (1 Corinthians 2:12-13)