It is not good for a Christian to doubt their salvation.
A Christian who is assured of their salvation will be a confident person in God’s Kingdom.
There are three forms of assurance:
 Believing and applying the Word of God.
For example, a Christian reads:
“Whoever believes in him is not condemned” John 3:18
They then apply this spiritual Truth to themselves, and that Truth fills them with an assurance of their salvation.
 Applying certain Biblical tests.
For example, when we read John’s first letter, we should then ask ourselves certain questions relating to what John was teaching:
“Do we love our fellow Christians? Do we love God’s commands?” etc.
If the answer is ‘yes’ then we have a greater assurance of salvation.
 Receiving the baptism of the Holy Spirit.
“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
This ‘sealing’ of the Spirit primarily gives assurance, because He guarantees our place in heaven.
The Holy Spirit fills us with an assurance of heaven.
If you want to know more about being filled with the Holy Spirit see an earlier post: