Three times Jesus tells His disciples these words. He has been sharing with these men how to act with humility and how to remember that God sees not only our acts but our heart's motives.
The first time He mentions these words is in regard to charitable deeds. It is better to quietly do or give rather than openly. He says, ...do not sound a trumpet...that you might receive glory from men...do not let your left hand know what your right is doing...
Then Jesus tells these men: ...your Father who sees in secret will reward you openly.
Likewise when praying it is not necessary to do so with fervor, flowery words or repetition to draw attention to self. It is to be done humbly, often in a quiet place, alone. Again, your Father who sees in secret will reward you openly.
And then when fasting it is not good to have the appearance of one who is. It draws attention to the individual. He says, yet a third time ...your Father who sees in secret will reward you. All we do in the quietness of our inner selves is what He sees and rewards.
Remember, Jesus came humbly into this world and He lived a humble life. He left this world in a tragic manner yet humbled Himself even then by not speaking up to defend Himself. He is to be our example of humility. I believe pride is the root of all our sin. It is not all about us but all about what our Father does in and through us and whether what we do is for self or for Him. We seem to have a problem with this pride, all of us.
Later in this chapter of Matthew Jesus is talking about where our treasures are, there's where our heart is. Is it all about Him or all about us? Are our hearts set on Him or our achievements and accomplishments? Do we give Him any glory for what He has done through us? Do we give Him any credit at all? Do we want recognition or do we want God to be seen in us? Do we shine His light or our own?
Jesus concludes by telling the disciples, as a teaching also for us, that we are not to worry about our lives because God's got a handle on it all. He's got the control if we allow Him. If we believe we must be in complete control, we've no faith in our Father in heaven. I look at the vitriol after this last presidential election. We need to understand that God is in control and He knows just what He is doing. If it means one side determined to go after the other, who knows what it might bring about in God's plan. Some will have faith in God, others will believe He has nothing to do with anything.
This God is the only means to life. We cannot do any more ourselves to bring life. He has complete control of our lives, even the number of hairs on our head, the number of our days. It is suggested we turn to Him and trust Him for that life. If we follow Him all our needs are met. Even if we do not have much, He supplies the necessities...the first being salvation of our souls with the end result being life everlasting. It's that life that is most important.
Apart from God we do not have this. Apart from God we will have our own reward, which amounts to very little. With God, we are secretly rewarded...a better reward than that which we receive from our own means.
Matthew 6:32-33 - For after all these things the Gentiles seek. For your heavenly Father knows that you need all these things. But seek first the kingdom of God and His righteousness, and all these things shall be added to you.