The first statement is the firm resolve of the Psalmist. He knows that joy and happiness are bound up with the Word of God. His purpose is to keep it.
The last statement is a plea that tempers the first with humility. He is not claiming a perfection and therefore cries to God that he not be forsaken. There is assurance and rest in God’s faithfulness. It is not the Psalmist’s ability to “keep” the statutes that comfort him. It is God’s faithfulness that encourages his heart.
The whole first stanza teaches us that the Word is our life. We are to walk, keep, respect, and learn. It is not all head work, but also for our hearts and hands. We have here an idyllic picture and also the strong desire to so walk. Complete dependence on God is emphasized throughout the whole stanza.