Your pastor probably was referring to the words of the Apostle Paul, who wrote that sometimes "Satan himself masquerades as an angel of light" (2 Corinthians 11:14).
Note that the Bible doesn't say Satan is an angel of light; it says he only masquerades as an angel of light. In other words, sometimes Satan puts on a disguise (as it were), and makes it look like he actually stands for good instead of evil. When the devil offered to feed Jesus by turning rocks into bread, he was masquerading as one who wanted to do good–or as an angel of light (see Matthew 4:1-11).
But Satan is not an angel of good or of light; he is the opposite. Jesus said that Satan "was a murderer from the beginning, not holding to the truth, for there is no truth in him. When he lies, he speaks his native language, for he is a liar and the father of lies" (John 8:44). Satan will try to deceive us and make us think that his way is best–but it never is. Martin Luther rightly labeled him "the prince of darkness." Don't fall for his lies!
Yes, Satan is our foe–but never forget he will not win! By His cross and resurrection Christ has defeated Satan, and some day "the devil, who deceived them, (will be) thrown into the lake of burning sulfur ... for ever and ever" (Revelation 20:10). Whose side are you on?