Psalm 121:8 is a comforting and reassuring verse. Let's break down what it means:

"Yahweh will keep..." - This establishes that it's God (Yahweh) who is the protector and guardian.
"your going out and your coming in..." - This phrase is an idiom that encompasses all aspects of your life and activities. It's a way of saying "everything you do, everywhere you go, in all circumstances." It means your daily life, your work, your travels, your projects - everything.
"...from this time forward..." - This indicates that God's protection begins now, at this moment.
"...and forever more." - This promises that God's protection is not temporary; it's eternal and ongoing. It extends beyond the present into the indefinite future.

In essence, the verse promises comprehensive and unending divine protection and care. It means:

God watches over you constantly: Whether you're leaving your home or returning, God is aware and involved in your life.
God safeguards your activities: He protects you in all your endeavors, both big and small.
God's protection is perpetual: This isn't a one-time blessing; it's a continuous promise that stretches into eternity.
God is intimately involved in your life: He cares about the details and is present in every moment.

The Significance and Implications:

This verse offers great encouragement and hope, because you are guaranteed His protection. Some examples of how to apply this truth are:
Reassurance: Knowing God is watching over us and all the things we do, we can be comforted and not feel anxious when facing uncertainty.
Faith in Daily life: We can approach each day with confidence, trusting that God will guide and protect us.
Eternal Security: We can rest assured that God's love and protection will never cease.
Gratitude: Recognizing God's constant presence and care inspires gratitude and strengthens our relationship with Him.

In short, Psalm 121:8 is a beautiful promise of God's unwavering presence and protection in every aspect of our lives, now and forever.