Yielding to God's and man's law brings simplicity. Obedience narrows the options, leaving fewer choices. For example, God's chosen saints never have to agonize over dishonesty in business, for God's holy and spiritual law makes the choice abundantly clear. Yielding to God's law reduces conflict and strife.
The Amplified Classic edition adds the following clarifying details. My son, forget not my law or teaching, but let your heart keep my commandments; For length of days and years of a life [worth living] and tranquility [inward and outward and continuing through old age till death], these shall they add to you.