Our conduct, our words and actions, flow from what has taken root in our heart. This is why we have the well-known encouragement and warning in Proverbs.
23 Keep your heart with all diligence, For out of it spring the issues of life. Proverbs 4:23 (NKJV)
Jesus also addressed the need to guard our hearts.
33 “Either make the tree good and its fruit good, or else make the tree bad and its fruit bad; for a tree is known by its fruit. 34 Brood of vipers! How can you, being evil, speak good things? For out of the abundance of the heart the mouth speaks. 35 A good man out of the good treasure of his heart brings forth good things, and an evil man out of the evil treasure brings forth evil things. 36 But I say to you that for every idle word men may speak, they will give account of it in the day of judgment. 37 For by your words you will be justified, and by your words you will be condemned.” Matthew 12:33-37 (NKJV)
Jesus focus on our words and their source but the application is broader as He contrasts good and evil ‘things’ coming out of our hearts. In the only Psalm we have by Moses we have a succinct summation of how we keep or guard our hearts.
12 So teach us to number our days, That we may gain a heart of wisdom. Psalm 90:12 (NKJV)
The New American Standard Bible translates the latter phrase of this verse a bit differently.
12 So teach us to number our days, That we may present to You a heart of wisdom. Psalm 90:12 (NASB)
Inherent in the common Hebrew verb bôʾ (gain/present) is the idea of both gaining and presenting. If we gain a heart of wisdom we can then present it to the Lord at the end of our days. The focus is on numbering our days to develop a wise heart. When we number our days we pay attention to how we invest our time and energy. Paul captured the concept in Ephesians 5:15-16 when he addressed the need to walk circumspectly and use our time wisely.
Given we do not know how many days we have on the earth we are wise if we number them. At my age I know I have many more days behind me then I do ahead of me and I want to be a good steward of my time. That doesn’t mean spending every waking moment praying or reading the scriptures. It does mean keeping at the forefront of my mind that I need to walk close to His heart throughout the day. It means allowing my heart to be drawn into intercession throughout the day. It means I need to be sensitive to His leading and calling and recognize that any relationship I engage in, however fleeting, I am an ambassador for Jesus, a representative of the King.