It says in Mark:
Mark 1:14-15
14 Jesus came to Galilee, proclaiming the Good News of God, and saying, 15 “The time is fulfilled, and the kingdom of God has come near; repent, and believe in the Good News”.
This is what it boils down to, a person’s belief in the Good News, which is to believe Jesus is our Lord and Saviour in order for us to enter Heaven:
Romans 10:9
If you declare with your mouth, “Jesus is Lord,” and believe in your heart that God raised him from the dead, you will be saved.
It’s our belief in Jesus that can save us but this is no guarantee we will receive the Holy Spirit:
Acts 19:2
"Did you receive the Holy Spirit when you believed?" They answered, "No, we have not even heard that there is a Holy Spirit."
If you wish to receive the Holy Spirit and deepen your relationship with Jesus and God the Father, thus ‘sealing’ your place in Heaven, you should also repent and be baptised:
Act 2:38
Peter replied, “Repent, and be baptised, every one of you, in the name of Jesus Christ for the forgiveness of your sins. And you will receive the gift of the Holy Spirit.”
Therefore, the three things we are commanded to do in order to receive the Holy Spirit are:
1. Believe in Jesus as our risen saviour.
2. Repent of our sins.
3. Get baptised.
After all, the first thing Jesus did in His ministry was to get baptised.
Therefore, Christians should do as He commanded by repenting of their sins and getting baptised in water, in the prayerful expectation of receiving the Holy Spirit:
John 3:5
Jesus answered, “Very truly I tell you, no one can enter the kingdom of God unless they are born of water, and the Spirit”.
This is important because Christians can lose there faith:
1 Timothy 6:10
For the love of money is a root of all kinds of evil. Some people, eager for money, have wandered from the faith and pierced themselves with many griefs.
James 5:19-20
19 My brothers and sisters, if one of you should wander from the truth and someone should bring that person back,20 remember this: Whoever turns a sinner from the error of their way will save them from death and cover over a multitude of sins.