YOU need to know that you belong to Him.
There are things that accompany salvation that signify that you have a saving relationship with God:
"9But, beloved, we are convinced of better things concerning you, and things that accompany salvation, though we are speaking in this way. 10For God is not unjust so as to forget your work and the love which you have shown toward His name, in having ministered and in still ministering to the saints. 11And we desire that each one of you show the same diligence so as to realize the full assurance of hope until the end, 12so that you will not be sluggish, but imitators of those who through faith and patience inherit the promises." - Hebrews 6:9-12
If you have those things, and are continuing in those things, then you know that you belong to Him.
If you don't have them, or are not continuing in them, you may not belong to Him at all.
You need to know for sure
before Jesus returns.
You may never know you are saved for sure if you take false comfort in some misguided 'I don't have to do anything' doctrine of assurance.
Not having works of righteousness is actually where fear and lack of assurance comes from.
Diligence in works gives the believer full assurance of salvation right to the very end of life.
No works leaves the 'believer' wondering in lack of assurance if they really have Christ in them in salvation.