Can't get past user login before MacBook reboots

Try booting in Safe Mode

Hold Shift right after your hear the Mac startup chime, for a few seconds, then release and wait for your MBP to power up safe mode, if it starts up normally then try rebooting normally and the issue will have been fixed.

in the case that the problem persists, you may want to try and boot holding Cmd+R for recovery mode, and then select Disk Utility from the Utilities menu, and attempt to first aid / repair your startup disksI hope you get it all fixed.