(This is the same post from last year. The Ash Wednesday readings are always the same, so the reflection is just as useful.)
I would like to focus simply on the Gospel reading today, Matthew 6:1-6, 16-18, and its intersection with another passage from the same Evangelist in the previous chapter, Matthew 5:13-16.
In the earlier passage, Matthew records these words of the Lord: "You are the light of the world. [...] your light must shine before others, that they may see your good deeds and glorify your heavenly Father." (Matthew 5:14,16), but in the later passage, we hear these words: "Take care not to perform righteous deeds in order that people may see them." (Matthew 6:1). Clearly these must resolve. Jesus has given us two instructions that do not contradict each other, but the second clarifies the first.
We are to let our light -- that is, the light of Christ in us -- shine before others, that they may see our good deeds and glorify God, not us. We are not to perform our deeds of righteousness in vanity so that others may see them and notice us. The hypocrites Jesus speaks of crave the attention and admiration of people, and that is their reward. But Jesus instructs us to seek the Father who will bestow His reward to us.
Jesus doesn't tell us to cover up our religion, to be ashamed of our faith, to keep our beliefs secret; on the contrary, we are to perform deeds of righteousness so that the light in us shines. But he does tell us to remember that the glory is God's, not ours. It is God who will glorify us, not ourselves and not the onlookers. It is God's reward that is everlasting. We are never to perform deeds for the attention of men... or that will be all we receive. We are instead to perform our deeds to give glory to God the Father, God the Son, and God the Holy Spirit.