Psalm 61  David is without doubt a true worshipper of God.  This psalm expresses his heart for and his confidence in his Lord:

You are my refuge, my "tower of strength against the enemy." 
" Let me dwell in Thy tent forever; Let me take refuge in the shelter of Thy wings." 
You have heard me.
You have given me... an inheritance.
You will prolong the King's life.
"He will abide before God forever";

"I will sing praise to Thy name forever, that I may pay my vows day by day." 

The phrase " pay my vows" is used in many of David's psalms - 22:25;56:12; 50:14; 65:1;  and 76:11
which tells us to "make vows and fulfill them".  
Deuteronomy 23:21-23  states, " When you make a vow to the Lord your God, you shall not delay to pay it, for it would be sin in you, and the Lord your God will surely require it of you. However if you refrain from vowing, it would not be sin in you. You shall be careful to perform what goes from your lips, just as you have voluntarily vowed to the Lord your God, what you have promised." 

Jesus has a word for us on this topic in Matthew 5,  " Again you have heard that the ancients were told, 'You shall not make false vows, but shall fulfill your vows to the Lord.'  But I say to you, make no oath at all, either by heaven for it is the throne of God, or by the earth, for it is the footstool of His feet, or by Jerusalem, for it is the city of the Great King.  Nor shall you make an oath by your head, for you cannot make one hair white or black.  But let your statement be, 'Yes, yes' or 'No,no' and beyond these is of evil. " 

 Vows and oaths are serious things.  When we make a promise to God and we do not complete it, then it is a sin.  Jesus instructs us to speak the truth always and to not bind ourselves to an oath that we cannot complete.

We do not know what all vows David has made to the Lord, but we see that he intends on fulfilling his every promise.  Foremost on his mind seems to be his promise to worship God forever. In fact he will do this "day by day".  In Psalm 145:2 he wrote, " Every day I will bless Thee, and I will praise Thy name forever and ever." 

We need to stop and examine our own hearts and minds... what promises have we made to the Lord our God?  Have we done what we promised?  What words have come from my own lips that He will hold me accountable for?

A few things that come to my mind:
I have said that I will trust in the Lord and lean not on my own understanding, that I will acknowledge Him in all my ways... am I doing that?
I have said that I will surrender all to Him, that I will lay down my life and take up my cross and follow Him.  Oh Lord, help me to do that day by day!
I have said that I will worship Him, love Him, serve Him... can I say that I am doing this?

Father of mercy and love,  hear my heart's cry, "lead me to the rock that is higher than I".  Let me dwell in Your presence and find refuge under Your wings.  You have heard my vows, my words, my promises to You... help me to complete them faithfully every day that I might abide with You forever.
Praise to You, my God and King, who looks with lovingkindness at Your beloved children, and shows infinite, glorious, grace.  Amen.