See what Jesus said in Matthew 5:48. This is the summation of the preceding verses in which He’d been explaining about how all God’s commandments were meant to be obeyed not merely in outward behavior (e.g. do not murder a person) but, more importantly, in inward motivations (e.g. don’t even think evil of them in your heart).
See also what the apostle John says about being able to recognize Jesus in 1 John 3:2.