The “security of the believer” is the unchanging objective reality that God has forgiven us and has accepted us through Jesus Christ forever.
The “assurance of the believer” is the sometimes shifting subjective confidence that God has forgiven us and has accepted us through Jesus Christ.
Do you have assurance? And do you have good reason to have it?
Faith is assurance, true, yet the faith of real believers is sometimes weak allowing doubts for a variety of reasons. An active enemy seeks to promote those doubts. Personality traits can play a part, and dramatic experiences or habitual sin can be factors. In some people doubts are well-founded and are useful to lead them to Christ. But it is not unusual for anyone to experience them. God wants all of his children to have assurance however and has provided several ways to obtain it.
Meditation on God’s promises, growth through trials, encouragement of other believers, genuine love for others, love for obedience, growth in holiness, answers to prayer, accumulative experience with God over time, persistent valuing of God and those things related to him, appreciation of the Bible and growing desire to read it, and the display of his fatherly care including correction, all serve to assure the believer. Welcome, and pursue these things.
If you cannot get perspective, talk with your pastor or a family member or friend who will be truthful with you to help you see more accurately.
God will not let you go if you are truly his. Be sure if this: God wants his children to have unshakable assurance.