Free trade must be fair, and must work for people, not just businesses.
The EU single market rules are underpinned by a strong core of social rights, both for workers and for people in general: to promote their general welfare, to facilitate freedom of movement by ensuring that accrued rights are portable and can travel with you to another country, and to prevent unscrupulous employers from exploiting national differences to undercut working conditions and the standard of living.
If you move to another EU country, EU rules on social security coordination guarantee you will not lose the rights which you accrued in your country of origin (i.e. you will not have to start from scratch) and you will be entitled to access to the social security system of your new country on the same terms as citizens of that country. So, if you retire to Spain, your pension will still be paid to you.
Click here to see what rights you have.